Dustbowl megabattle
Looks like we've got a third megabattle on our hands, and in level 3 of all places! It takes place in the dustbowl area: the big area with a rocky bridge over a bowl-like depression. Amazingly you can have up to 50 enemies there, made up from the usuals plus enemies from earlier on, who you've encouraged along. They'll all chase you around, which lets you lead them to good places to defend from, do a progressive defence on the move, or whatever. It's also great for chain reactions and general mayhem.
As well as some intense battling, you can have some hilarious fun with up to 32 Grunts chasing around after you, surely the biggest gaggle in the game. You should see those critters swarm! If you want a megabattle that makes you laugh, this is it.
The first page covers setting up, including a quick-start basic plan to get you going. There's a much more detailed plan you can delve into later if you want to get more refined. The second page chats about the battling and fun you can have.