A new playable character (Apollyon)
67 new items, 27 new trinkets and 10+ new pickups
A new final chapter
A new final boss
62 new achievements
5 achievement 'challenges'
100s of new rooms!
New victory lap feature! (allows the game to continue when finished)
A bestiary showing you a lot of detail related to the enemies you encounter throughout the game
2 new transformations
Monthly content updates (game will be updated with community made mods)
4+ new bosses and a new alt forms for existing bosses!
In terms of modding tools, you can expect the following mod support to be included in this DLC:
A LUA modding API
Official room editor
Animation editor
Item pool editor
Custom challenge creator