The whole manual, open to read before you start — every stat, curve, drop rate and rule the game runs on. Nothing here is hidden from new players.
Stuck on a stage? Leave a SHADOW on it. Open the stage’s card on the Battle map and press Leave a Shadow. It fights that stage for you, one attempt every 6 minutes, whether you are on the page, elsewhere, or logged out. Every win pushes the stage, and the Shadow carries on against the next level.
A Shadow and Mercenaries cannot share a stage. The Shadow pushes stages you cannot beat yet; Mercenaries farm stages you cleared. With the Shadow Army pack, dropping a Mercenary on a stage makes the Shadow there settle up and step aside, returning when the Mercenary leaves.