diff --git a/BaseClasses.py b/BaseClasses.py
index af1f2180..5dcc9daa 100644
--- a/BaseClasses.py
+++ b/BaseClasses.py
@@ -325,15 +325,15 @@ class MultiWorld():
     def player_ids(self) -> Tuple[int, ...]:
         return tuple(range(1, self.players + 1))
 
-    @functools.lru_cache()
+    @Utils.cache_self1
     def get_game_players(self, game_name: str) -> Tuple[int, ...]:
         return tuple(player for player in self.player_ids if self.game[player] == game_name)
 
-    @functools.lru_cache()
+    @Utils.cache_self1
     def get_game_groups(self, game_name: str) -> Tuple[int, ...]:
         return tuple(group_id for group_id in self.groups if self.game[group_id] == game_name)
 
-    @functools.lru_cache()
+    @Utils.cache_self1
     def get_game_worlds(self, game_name: str):
         return tuple(world for player, world in self.worlds.items() if
                      player not in self.groups and self.game[player] == game_name)
diff --git a/Generate.py b/Generate.py
index 34a0084e..8113d8a0 100644
--- a/Generate.py
+++ b/Generate.py
@@ -7,8 +7,8 @@ import random
 import string
 import urllib.parse
 import urllib.request
-from collections import ChainMap, Counter
-from typing import Any, Callable, Dict, Tuple, Union
+from collections import Counter
+from typing import Any, Dict, Tuple, Union
 
 import ModuleUpdate
 
@@ -225,7 +225,7 @@ def main(args=None, callback=ERmain):
         with open(os.path.join(args.outputpath if args.outputpath else ".", f"generate_{seed_name}.yaml"), "wt") as f:
             yaml.dump(important, f)
 
-    callback(erargs, seed)
+    return callback(erargs, seed)
 
 
 def read_weights_yamls(path) -> Tuple[Any, ...]:
@@ -639,6 +639,15 @@ def roll_alttp_settings(ret: argparse.Namespace, weights, plando_options):
 if __name__ == '__main__':
     import atexit
     confirmation = atexit.register(input, "Press enter to close.")
-    main()
+    multiworld = main()
+    if __debug__:
+        import gc
+        import sys
+        import weakref
+        weak = weakref.ref(multiworld)
+        del multiworld
+        gc.collect()  # need to collect to deref all hard references
+        assert not weak(), f"MultiWorld object was not de-allocated, it's referenced {sys.getrefcount(weak())} times." \
+                           " This would be a memory leak."
     # in case of error-free exit should not need confirmation
     atexit.unregister(confirmation)
diff --git a/Utils.py b/Utils.py
index 4cf8ca22..114c2e81 100644
--- a/Utils.py
+++ b/Utils.py
@@ -74,6 +74,8 @@ def snes_to_pc(value: int) -> int:
 
 
 RetType = typing.TypeVar("RetType")
+S = typing.TypeVar("S")
+T = typing.TypeVar("T")
 
 
 def cache_argsless(function: typing.Callable[[], RetType]) -> typing.Callable[[], RetType]:
@@ -91,6 +93,31 @@ def cache_argsless(function: typing.Callable[[], RetType]) -> typing.Callable[[]
     return _wrap
 
 
+def cache_self1(function: typing.Callable[[S, T], RetType]) -> typing.Callable[[S, T], RetType]:
+    """Specialized cache for self + 1 arg. Does not keep global ref to self and skips building a dict key tuple."""
+
+    assert function.__code__.co_argcount == 2, "Can only cache 2 argument functions with this cache."
+
+    cache_name = f"__cache_{function.__name__}__"
+
+    @functools.wraps(function)
+    def wrap(self: S, arg: T) -> RetType:
+        cache: Optional[Dict[T, RetType]] = typing.cast(Optional[Dict[T, RetType]],
+                                                        getattr(self, cache_name, None))
+        if cache is None:
+            res = function(self, arg)
+            setattr(self, cache_name, {arg: res})
+            return res
+        try:
+            return cache[arg]
+        except KeyError:
+            res = function(self, arg)
+            cache[arg] = res
+            return res
+
+    return wrap
+
+
 def is_frozen() -> bool:
     return typing.cast(bool, getattr(sys, 'frozen', False))
 
diff --git a/test/bases.py b/test/bases.py
index 9911a45b..2054c2d1 100644
--- a/test/bases.py
+++ b/test/bases.py
@@ -1,3 +1,4 @@
+import sys
 import typing
 import unittest
 from argparse import Namespace
@@ -107,11 +108,36 @@ class WorldTestBase(unittest.TestCase):
     game: typing.ClassVar[str]  # define game name in subclass, example "Secret of Evermore"
     auto_construct: typing.ClassVar[bool] = True
     """ automatically set up a world for each test in this class """
+    memory_leak_tested: typing.ClassVar[bool] = False
+    """ remember if memory leak test was already done for this class """
 
     def setUp(self) -> None:
         if self.auto_construct:
             self.world_setup()
 
+    def tearDown(self) -> None:
+        if self.__class__.memory_leak_tested or not self.options or not self.constructed or \
+                sys.version_info < (3, 11, 0):  # the leak check in tearDown fails in py<3.11 for an unknown reason
+            # only run memory leak test once per class, only for constructed with non-default options
+            # default options will be tested in test/general
+            super().tearDown()
+            return
+
+        import gc
+        import weakref
+        weak = weakref.ref(self.multiworld)
+        for attr_name in dir(self):  # delete all direct references to MultiWorld and World
+            attr: object = typing.cast(object, getattr(self, attr_name))
+            if type(attr) is MultiWorld or isinstance(attr, AutoWorld.World):
+                delattr(self, attr_name)
+        state_cache: typing.Optional[typing.Dict[typing.Any, typing.Any]] = getattr(self, "_state_cache", None)
+        if state_cache is not None:  # in case of multiple inheritance with TestBase, we need to clear its cache
+            state_cache.clear()
+        gc.collect()
+        self.__class__.memory_leak_tested = True
+        self.assertFalse(weak(), f"World {getattr(self, 'game', '')} leaked MultiWorld object")
+        super().tearDown()
+
     def world_setup(self, seed: typing.Optional[int] = None) -> None:
         if type(self) is WorldTestBase or \
                 (hasattr(WorldTestBase, self._testMethodName)
diff --git a/test/general/test_memory.py b/test/general/test_memory.py
new file mode 100644
index 00000000..e352b9e8
--- /dev/null
+++ b/test/general/test_memory.py
@@ -0,0 +1,16 @@
+import unittest
+
+from worlds.AutoWorld import AutoWorldRegister
+from . import setup_solo_multiworld
+
+
+class TestWorldMemory(unittest.TestCase):
+    def test_leak(self):
+        """Tests that worlds don't leak references to MultiWorld or themselves with default options."""
+        import gc
+        import weakref
+        for game_name, world_type in AutoWorldRegister.world_types.items():
+            with self.subTest("Game", game_name=game_name):
+                weak = weakref.ref(setup_solo_multiworld(world_type))
+                gc.collect()
+                self.assertFalse(weak(), "World leaked a reference")
diff --git a/test/utils/test_caches.py b/test/utils/test_caches.py
new file mode 100644
index 00000000..fc681611
--- /dev/null
+++ b/test/utils/test_caches.py
@@ -0,0 +1,66 @@
+# Tests for caches in Utils.py
+
+import unittest
+from typing import Any
+
+from Utils import cache_argsless, cache_self1
+
+
+class TestCacheArgless(unittest.TestCase):
+    def test_cache(self) -> None:
+        @cache_argsless
+        def func_argless() -> object:
+            return object()
+
+        self.assertTrue(func_argless() is func_argless())
+
+    if __debug__:  # assert only available with __debug__
+        def test_invalid_decorator(self) -> None:
+            with self.assertRaises(Exception):
+                @cache_argsless  # type: ignore[arg-type]
+                def func_with_arg(_: Any) -> None:
+                    pass
+
+
+class TestCacheSelf1(unittest.TestCase):
+    def test_cache(self) -> None:
+        class Cls:
+            @cache_self1
+            def func(self, _: Any) -> object:
+                return object()
+
+        o1 = Cls()
+        o2 = Cls()
+        self.assertTrue(o1.func(1) is o1.func(1))
+        self.assertFalse(o1.func(1) is o1.func(2))
+        self.assertFalse(o1.func(1) is o2.func(1))
+
+    def test_gc(self) -> None:
+        # verify that we don't keep a global reference
+        import gc
+        import weakref
+
+        class Cls:
+            @cache_self1
+            def func(self, _: Any) -> object:
+                return object()
+
+        o = Cls()
+        _ = o.func(o)  # keep a hard ref to the result
+        r = weakref.ref(o)  # keep weak ref to the cache
+        del o  # remove hard ref to the cache
+        gc.collect()
+        self.assertFalse(r())  # weak ref should be dead now
+
+    if __debug__:  # assert only available with __debug__
+        def test_no_self(self) -> None:
+            with self.assertRaises(Exception):
+                @cache_self1  # type: ignore[arg-type]
+                def func() -> Any:
+                    pass
+
+        def test_too_many_args(self) -> None:
+            with self.assertRaises(Exception):
+                @cache_self1  # type: ignore[arg-type]
+                def func(_1: Any, _2: Any, _3: Any) -> Any:
+                    pass
diff --git a/worlds/sm/__init__.py b/worlds/sm/__init__.py
index 4b4002c1..e85d79d3 100644
--- a/worlds/sm/__init__.py
+++ b/worlds/sm/__init__.py
@@ -112,15 +112,12 @@ class SMWorld(World):
     required_client_version = (0, 2, 6)
 
     itemManager: ItemManager
-    spheres = None
 
     Logic.factory('vanilla')
 
     def __init__(self, world: MultiWorld, player: int):
         self.rom_name_available_event = threading.Event()
         self.locations = {}
-        if SMWorld.spheres != None:
-            SMWorld.spheres = None
         super().__init__(world, player)
 
     @classmethod
@@ -368,7 +365,7 @@ class SMWorld(World):
                                     locationsDict[first_local_collected_loc.name]),
                         itemLoc.item.player,
                         True)
-                        for itemLoc in SMWorld.spheres if itemLoc.item.player == self.player and (not progression_only or itemLoc.item.advancement)
+                        for itemLoc in spheres if itemLoc.item.player == self.player and (not progression_only or itemLoc.item.advancement)
                     ]
         
         # Having a sorted itemLocs from collection order is required for escapeTrigger when Tourian is Disabled.
@@ -376,8 +373,10 @@ class SMWorld(World):
         # get_spheres could be cached in multiworld?
         # Another possible solution would be to have a globally accessible list of items in the order in which the get placed in push_item
         # and use the inversed starting from the first progression item.
-        if (SMWorld.spheres == None):
-            SMWorld.spheres = [itemLoc for sphere in self.multiworld.get_spheres() for itemLoc in sorted(sphere, key=lambda location: location.name)]
+        spheres: List[Location] = getattr(self.multiworld, "_sm_spheres", None)
+        if spheres is None:
+            spheres = [itemLoc for sphere in self.multiworld.get_spheres() for itemLoc in sorted(sphere, key=lambda location: location.name)]
+            setattr(self.multiworld, "_sm_spheres", spheres)
 
         self.itemLocs = [
             ItemLocation(copy.copy(ItemManager.Items[itemLoc.item.type