Hardcore

Hardcore Mode! is a selectable option on campaign maps, including Survival and Pure Strategy.

What is Hardcore?
When Hardcore mode is selected, players lose the ability to respawn during the Combat Phase, and must wait until the next Build Phase to return. The wave will continue to play out, even after all players are dead, until either the wave finishes, or the Eternia Crystal is destroyed, whichever comes first.

In the event that you die during the Build Phase, and the Combat Phase begins before you respawn, you will not respawn until the next Build Phase.

Why play it?
A game with Hardcore mode enabled will give better loot and experience compared to a standard game, provided you survive!

Hardcore mode yields a 30% Bonus EXP at the end of each wave, regardless of difficulty.

(From original Dungeon Defenders wiki).