diff --git a/tianshou/highlevel/agent.py b/tianshou/highlevel/agent.py
index f9e493b..6cc43d9 100644
--- a/tianshou/highlevel/agent.py
+++ b/tianshou/highlevel/agent.py
@@ -1,4 +1,5 @@
 import logging
+import typing
 from abc import ABC, abstractmethod
 from typing import Any, Generic, TypeVar, cast
 
@@ -63,11 +64,17 @@ from tianshou.utils.string import ToStringMixin
 CHECKPOINT_DICT_KEY_MODEL = "model"
 CHECKPOINT_DICT_KEY_OBS_RMS = "obs_rms"
 TParams = TypeVar("TParams", bound=Params)
-TActorCriticParams = TypeVar("TActorCriticParams", bound=ParamsMixinLearningRateWithScheduler)
-TActorDualCriticsParams = TypeVar("TActorDualCriticsParams", bound=ParamsMixinActorAndDualCritics)
+TActorCriticParams = TypeVar(
+    "TActorCriticParams",
+    bound=Params | ParamsMixinLearningRateWithScheduler,
+)
+TActorDualCriticsParams = TypeVar(
+    "TActorDualCriticsParams",
+    bound=Params | ParamsMixinActorAndDualCritics,
+)
 TDiscreteCriticOnlyParams = TypeVar(
     "TDiscreteCriticOnlyParams",
-    bound=ParamsMixinLearningRateWithScheduler,
+    bound=Params | ParamsMixinLearningRateWithScheduler,
 )
 TPolicy = TypeVar("TPolicy", bound=BasePolicy)
 log = logging.getLogger(__name__)
@@ -321,6 +328,7 @@ class ActorCriticAgentFactory(
         optim = self.optim_factory.create_optimizer(actor_critic, lr)
         return ActorCriticModuleOpt(actor_critic, optim)
 
+    @typing.no_type_check
     def _create_kwargs(self, envs: Environments, device: TDevice) -> dict[str, Any]:
         actor_critic = self.create_actor_critic_module_opt(envs, device, self.params.lr)
         kwargs = self.params.create_kwargs(
@@ -382,6 +390,7 @@ class DiscreteCriticOnlyAgentFactory(
     def _get_policy_class(self) -> type[TPolicy]:
         pass
 
+    @typing.no_type_check
     def _create_policy(self, envs: Environments, device: TDevice) -> TPolicy:
         model = self.model_factory.create_module(envs, device)
         optim = self.optim_factory.create_optimizer(model, self.params.lr)
@@ -548,6 +557,7 @@ class ActorDualCriticsAgentFactory(
     def _get_critic_use_action(envs: Environments) -> bool:
         return envs.get_type().is_continuous()
 
+    @typing.no_type_check
     def _create_policy(self, envs: Environments, device: TDevice) -> TPolicy:
         actor = self.actor_factory.create_module_opt(
             envs,
diff --git a/tianshou/highlevel/env.py b/tianshou/highlevel/env.py
index 179f941..f356f4d 100644
--- a/tianshou/highlevel/env.py
+++ b/tianshou/highlevel/env.py
@@ -37,7 +37,7 @@ class Environments(ToStringMixin, ABC):
         self.env = env
         self.train_envs = train_envs
         self.test_envs = test_envs
-        self.persistence = []
+        self.persistence: Sequence[Persistence] = []
 
     def _tostring_includes(self) -> list[str]:
         return []
@@ -51,7 +51,7 @@ class Environments(ToStringMixin, ABC):
             "state_shape": self.get_observation_shape(),
         }
 
-    def set_persistence(self, *p: Persistence):
+    def set_persistence(self, *p: Persistence) -> None:
         self.persistence = p
 
     @abstractmethod
diff --git a/tianshou/highlevel/experiment.py b/tianshou/highlevel/experiment.py
index 8394111..a5c72f0 100644
--- a/tianshou/highlevel/experiment.py
+++ b/tianshou/highlevel/experiment.py
@@ -27,7 +27,7 @@ from tianshou.highlevel.agent import (
 )
 from tianshou.highlevel.config import SamplingConfig
 from tianshou.highlevel.env import EnvFactory, Environments
-from tianshou.highlevel.logger import DefaultLoggerFactory, LoggerFactory
+from tianshou.highlevel.logger import DefaultLoggerFactory, LoggerFactory, TLogger
 from tianshou.highlevel.module.actor import (
     ActorFactory,
     ActorFactoryDefault,
@@ -142,13 +142,18 @@ class Experiment(Generic[TPolicy, TTrainer], ToStringMixin):
         self.env_config = env_config
 
     @classmethod
-    def from_directory(cls, directory: str) -> Self:
+    def from_directory(cls, directory: str, restore_policy: bool = True) -> Self:
         """Restores an experiment from a previously stored pickle.
 
         :param directory: persistence directory of a previous run, in which a pickled experiment is found
+        :param restore_policy: whether the experiment shall be configured to restore the policy that was
+            persisted in the given directory
         """
         with open(os.path.join(directory, cls.EXPERIMENT_PICKLE_FILENAME), "rb") as f:
-            return pickle.load(f)
+            experiment: Experiment = pickle.load(f)
+        if restore_policy:
+            experiment.config.policy_restore_directory = directory
+        return experiment
 
     def _set_seed(self) -> None:
         seed = self.config.seed
@@ -159,7 +164,7 @@ class Experiment(Generic[TPolicy, TTrainer], ToStringMixin):
     def _build_config_dict(self) -> dict:
         return {"experiment": self.pprints()}
 
-    def save(self, directory: str):
+    def save(self, directory: str) -> None:
         path = os.path.join(directory, self.EXPERIMENT_PICKLE_FILENAME)
         log.info(
             f"Saving serialized experiment in {path}; can be restored via Experiment.from_directory('{directory}')",
@@ -187,7 +192,8 @@ class Experiment(Generic[TPolicy, TTrainer], ToStringMixin):
             os.makedirs(persistence_dir, exist_ok=True)
 
         with logging.FileLoggerContext(
-            os.path.join(persistence_dir, self.LOG_FILENAME), enabled=use_persistence,
+            os.path.join(persistence_dir, self.LOG_FILENAME),
+            enabled=use_persistence,
         ):
             # log initial information
             log.info(f"Running experiment (name='{experiment_name}'):\n{self.pprints()}")
@@ -209,6 +215,7 @@ class Experiment(Generic[TPolicy, TTrainer], ToStringMixin):
             # initialize logger
             full_config = self._build_config_dict()
             full_config.update(envs.info())
+            logger: TLogger
             if use_persistence:
                 logger = self.logger_factory.create_logger(
                     log_dir=persistence_dir,
@@ -460,7 +467,7 @@ class _BuilderMixinCriticsFactory:
 
 
 class _BuilderMixinSingleCriticFactory(_BuilderMixinCriticsFactory):
-    def __init__(self, actor_future_provider: ActorFutureProviderProtocol = None) -> None:
+    def __init__(self, actor_future_provider: ActorFutureProviderProtocol) -> None:
         super().__init__(1, actor_future_provider)
 
     def with_critic_factory(self, critic_factory: CriticFactory) -> Self:
@@ -553,7 +560,7 @@ class _BuilderMixinCriticEnsembleFactory:
         self.critic_ensemble_factory = CriticEnsembleFactoryDefault(hidden_sizes)
         return self
 
-    def _get_critic_ensemble_factory(self):
+    def _get_critic_ensemble_factory(self) -> CriticEnsembleFactory:
         if self.critic_ensemble_factory is None:
             return CriticEnsembleFactoryDefault()
         else:
@@ -745,8 +752,10 @@ class IQNExperimentBuilder(ExperimentBuilder):
     ):
         super().__init__(env_factory, experiment_config, sampling_config)
         self._params: IQNParams = IQNParams()
-        self._preprocess_network_factory = IntermediateModuleFactoryFromActorFactory(
-            ActorFactoryDefault(ContinuousActorType.UNSUPPORTED),
+        self._preprocess_network_factory: IntermediateModuleFactory = (
+            IntermediateModuleFactoryFromActorFactory(
+                ActorFactoryDefault(ContinuousActorType.UNSUPPORTED),
+            )
         )
 
     def with_iqn_params(self, params: IQNParams) -> Self:
diff --git a/tianshou/highlevel/logger.py b/tianshou/highlevel/logger.py
index 6260977..c10599a 100644
--- a/tianshou/highlevel/logger.py
+++ b/tianshou/highlevel/logger.py
@@ -4,16 +4,20 @@ from typing import Literal, TypeAlias
 
 from torch.utils.tensorboard import SummaryWriter
 
-from tianshou.utils import TensorboardLogger, WandbLogger
+from tianshou.utils import BaseLogger, TensorboardLogger, WandbLogger
 from tianshou.utils.string import ToStringMixin
 
-TLogger: TypeAlias = TensorboardLogger | WandbLogger
+TLogger: TypeAlias = BaseLogger
 
 
 class LoggerFactory(ToStringMixin, ABC):
     @abstractmethod
     def create_logger(
-        self, log_dir: str, experiment_name: str, run_id: str | None, config_dict: dict,
+        self,
+        log_dir: str,
+        experiment_name: str,
+        run_id: str | None,
+        config_dict: dict,
     ) -> TLogger:
         """:param log_dir: path to the directory in which log data is to be stored
         :param experiment_name: the name of the job, which may contain os.path.sep
@@ -35,7 +39,11 @@ class DefaultLoggerFactory(LoggerFactory):
         self.wandb_project = wandb_project
 
     def create_logger(
-        self, log_dir: str, experiment_name: str, run_id: str | None, config_dict: dict,
+        self,
+        log_dir: str,
+        experiment_name: str,
+        run_id: str | None,
+        config_dict: dict,
     ) -> TLogger:
         writer = SummaryWriter(log_dir)
         writer.add_text(
@@ -48,18 +56,18 @@ class DefaultLoggerFactory(LoggerFactory):
                 ),
             ),
         )
-        logger: TLogger
-        if self.logger_type == "wandb":
-            logger = WandbLogger(
-                save_interval=1,
-                name=experiment_name.replace(os.path.sep, "__"),
-                run_id=run_id,
-                config=config_dict,
-                project=self.wandb_project,
-            )
-            logger.load(writer)
-        elif self.logger_type == "tensorboard":
-            logger = TensorboardLogger(writer)
-        else:
-            raise ValueError(f"Unknown logger type '{self.logger_type}'")
-        return logger
+        match self.logger_type:
+            case "wandb":
+                wandb_logger = WandbLogger(
+                    save_interval=1,
+                    name=experiment_name.replace(os.path.sep, "__"),
+                    run_id=run_id,
+                    config=config_dict,
+                    project=self.wandb_project,
+                )
+                wandb_logger.load(writer)
+                return wandb_logger
+            case "tensorboard":
+                return TensorboardLogger(writer)
+            case _:
+                raise ValueError(f"Unknown logger type '{self.logger_type}'")
diff --git a/tianshou/highlevel/module/actor.py b/tianshou/highlevel/module/actor.py
index e02b280..d3f31f6 100644
--- a/tianshou/highlevel/module/actor.py
+++ b/tianshou/highlevel/module/actor.py
@@ -209,16 +209,16 @@ class ActorFactoryTransientStorageDecorator(ActorFactory):
         self.actor_factory = actor_factory
         self._actor_future = actor_future
 
-    def __getstate__(self):
+    def __getstate__(self) -> dict:
         d = dict(self.__dict__)
         del d["_actor_future"]
         return d
 
-    def __setstate__(self, state):
+    def __setstate__(self, state: dict) -> None:
         self.__dict__ = state
         self._actor_future = ActorFuture()
 
-    def _tostring_excludes(self):
+    def _tostring_excludes(self) -> list[str]:
         return [*super()._tostring_excludes(), "_actor_future"]
 
     def create_module(self, envs: Environments, device: TDevice) -> BaseActor | nn.Module:
diff --git a/tianshou/highlevel/module/critic.py b/tianshou/highlevel/module/critic.py
index 4af97bc..54b6003 100644
--- a/tianshou/highlevel/module/critic.py
+++ b/tianshou/highlevel/module/critic.py
@@ -1,6 +1,7 @@
 from abc import ABC, abstractmethod
 from collections.abc import Sequence
 
+import numpy as np
 from torch import nn
 
 from tianshou.highlevel.env import Environments, EnvType
@@ -61,7 +62,7 @@ class CriticFactoryDefault(CriticFactory):
         envs: Environments,
         device: TDevice,
         use_action: bool,
-        discrete_last_size_use_action_shape=False,
+        discrete_last_size_use_action_shape: bool = False,
     ) -> nn.Module:
         factory: CriticFactory
         env_type = envs.get_type()
@@ -89,7 +90,7 @@ class CriticFactoryContinuousNet(CriticFactory):
         envs: Environments,
         device: TDevice,
         use_action: bool,
-        discrete_last_size_use_action_shape=False,
+        discrete_last_size_use_action_shape: bool = False,
     ) -> nn.Module:
         action_shape = envs.get_action_shape() if use_action else 0
         net_c = Net(
@@ -114,7 +115,7 @@ class CriticFactoryDiscreteNet(CriticFactory):
         envs: Environments,
         device: TDevice,
         use_action: bool,
-        discrete_last_size_use_action_shape=False,
+        discrete_last_size_use_action_shape: bool = False,
     ) -> nn.Module:
         action_shape = envs.get_action_shape() if use_action else 0
         net_c = Net(
@@ -125,7 +126,9 @@ class CriticFactoryDiscreteNet(CriticFactory):
             activation=nn.Tanh,
             device=device,
         )
-        last_size = envs.get_action_shape() if discrete_last_size_use_action_shape else 1
+        last_size = (
+            int(np.prod(envs.get_action_shape())) if discrete_last_size_use_action_shape else 1
+        )
         critic = discrete.Critic(net_c, device=device, last_size=last_size).to(device)
         init_linear_orthogonal(critic)
         return critic
@@ -149,7 +152,7 @@ class CriticFactoryReuseActor(CriticFactory):
         envs: Environments,
         device: TDevice,
         use_action: bool,
-        discrete_last_size_use_action_shape=False,
+        discrete_last_size_use_action_shape: bool = False,
     ) -> nn.Module:
         actor = self.actor_future.actor
         if not isinstance(actor, BaseActor):
@@ -157,7 +160,10 @@ class CriticFactoryReuseActor(CriticFactory):
                 f"Option critic_use_action can only be used if actor is of type {BaseActor.__class__.__name__}",
             )
         if envs.get_type().is_discrete():
-            last_size = envs.get_action_shape() if discrete_last_size_use_action_shape else 1
+            # TODO get rid of this prod pattern here and elsewhere
+            last_size = (
+                int(np.prod(envs.get_action_shape())) if discrete_last_size_use_action_shape else 1
+            )
             return discrete.Critic(
                 actor.get_preprocess_net(),
                 device=device,
diff --git a/tianshou/highlevel/persistence.py b/tianshou/highlevel/persistence.py
index 225b1e8..fad4bea 100644
--- a/tianshou/highlevel/persistence.py
+++ b/tianshou/highlevel/persistence.py
@@ -45,12 +45,12 @@ class Persistence(ABC):
         pass
 
     @abstractmethod
-    def restore(self, event: RestoreEvent, world: World):
+    def restore(self, event: RestoreEvent, world: World) -> None:
         pass
 
 
 class PersistenceGroup(Persistence):
-    def __init__(self, *p: Persistence, enabled=True):
+    def __init__(self, *p: Persistence, enabled: bool = True):
         self.items = p
         self.enabled = enabled
 
@@ -60,7 +60,7 @@ class PersistenceGroup(Persistence):
         for item in self.items:
             item.persist(event, world)
 
-    def restore(self, event: RestoreEvent, world: World):
+    def restore(self, event: RestoreEvent, world: World) -> None:
         for item in self.items:
             item.restore(event, world)
 
@@ -68,7 +68,7 @@ class PersistenceGroup(Persistence):
 class PolicyPersistence:
     FILENAME = "policy.dat"
 
-    def __init__(self, additional_persistence: Persistence | None = None, enabled=True):
+    def __init__(self, additional_persistence: Persistence | None = None, enabled: bool = True):
         """:param additional_persistence: a persistence instance which is to be envoked whenever
             this object is used to persist/restore data
         :param enabled: whether persistence is enabled (restoration is always enabled)
@@ -93,7 +93,7 @@ class PolicyPersistence:
         if self.additional_persistence is not None:
             self.additional_persistence.restore(RestoreEvent.RESTORE_POLICY, world)
 
-    def get_save_best_fn(self, world) -> Callable[[torch.nn.Module], None]:
+    def get_save_best_fn(self, world: World) -> Callable[[torch.nn.Module], None]:
         def save_best_fn(pol: torch.nn.Module) -> None:
             self.persist(pol, world)
 
diff --git a/tianshou/highlevel/world.py b/tianshou/highlevel/world.py
index aa278db..6ec7c4b 100644
--- a/tianshou/highlevel/world.py
+++ b/tianshou/highlevel/world.py
@@ -18,7 +18,7 @@ class World:
     test_collector: "Collector"
     logger: "TLogger"
     persist_directory: str
-    restore_directory: str
+    restore_directory: str | None
     trainer: Optional["BaseTrainer"] = None
 
     def persist_path(self, filename: str) -> str:
diff --git a/tianshou/policy/modelfree/pg.py b/tianshou/policy/modelfree/pg.py
index fb7027b..c9f5ccc 100644
--- a/tianshou/policy/modelfree/pg.py
+++ b/tianshou/policy/modelfree/pg.py
@@ -17,7 +17,8 @@ from tianshou.policy import BasePolicy
 from tianshou.policy.base import TLearningRateScheduler
 from tianshou.utils import RunningMeanStd
 
-TDistributionFunction: TypeAlias = Callable[[torch.Tensor, ...], torch.distributions.Distribution]
+# TODO: Is there a better way to define this type? mypy doesn't like Callable[[torch.Tensor, ...], torch.distributions.Distribution]
+TDistributionFunction: TypeAlias = Callable[..., torch.distributions.Distribution]
 
 
 class PGPolicy(BasePolicy):
diff --git a/tianshou/utils/net/continuous.py b/tianshou/utils/net/continuous.py
index 60c3569..5595750 100644
--- a/tianshou/utils/net/continuous.py
+++ b/tianshou/utils/net/continuous.py
@@ -216,7 +216,7 @@ class ActorProb(BaseActor):
     def get_preprocess_net(self) -> nn.Module:
         return self.preprocess
 
-    def get_output_dim(self):
+    def get_output_dim(self) -> int:
         return self.output_dim
 
     def forward(
diff --git a/tianshou/utils/net/discrete.py b/tianshou/utils/net/discrete.py
index ccdd69d..1b5b019 100644
--- a/tianshou/utils/net/discrete.py
+++ b/tianshou/utils/net/discrete.py
@@ -189,7 +189,7 @@ class ImplicitQuantileNetwork(Critic):
     def __init__(
         self,
         preprocess_net: nn.Module,
-        action_shape: Sequence[int],
+        action_shape: Sequence[int] | int,
         hidden_sizes: Sequence[int] = (),
         num_cosines: int = 64,
         preprocess_net_output_dim: int | None = None,