"modify almost everything" in the game.
That includes fiddling with item and skill balances, level designs, animations, quests, "and much more," teased Runic. There's a conversion tool for old mods in this new era for Torchlight 2.
Steam Workshop provides a hub for the community through Steam where players can easily subscribe to what mods they'd like to play with, and Steam takes care of it.
Runic has released new NetherRealm content which is accessible through game world portals, and they include new monsters, gear and even a headcrab pet in honour of Valve's Half-Life. The official Torchlight 2 website has a, which helps expand on just what can be accomplished.