Mellow Rib
A Sandbox level for DK1 where you control Bridges and can pit your 2 Keeper opponents against each other or the Heroes. You can ignore the Keepers as well and simply destroy the Hero Dungeon Heart, just watch out for the Avatar. Use various Rooms to adjust the difficulty of the Hero Spawns.
For KeeperFX, you can find it under Campaigns, called "Sandbox Level"
Room Size References
Barracks - set the Strength of the Hero Parties.
Defaults to a level 5 party of Five Heroes.
16 tiles summons a level 7-8 party of Six Heroes.
25 tiles summons a level 7-8 party of Seven Heroes.
30 tiles summons a level 10 party of Six Heroes.
36 tiles summons a level 10 party of Seven Heroes.
49 will summon the Avatar and his Goons.
Torture Chamber - sets the spawns at 2 locations near your Dungeon Heart
Defaults to no summons in the South.
30 tiles will spawn from the Southwest.
36 tiles will spawn from both Southwest and Southeast.
Temple - sets the Time interval before each Hero Party spawns
Defaults to the Hero Party never spawning.
25 tiles spawn at 20 minute intervals.
30 tiles spawn at 10 minute intervals.
36 tiles spawn at 1 minute intervals, as good as instantly.