Survival is a game mode that increases the number of waves to at least 25 for all mission maps. The waves gets increasingly harder. Survival can be played on any difficulty, provided that the player has already cleared the map on that difficulty in the campaign.
This game mode is high rewarding and is a good way to prepare for maps of greater difficulty or for maps that seems to be unbeatable. The equipment will on higher wave-levels be significantly better than the equipment that is dropped on the same difficulty in the campaign.
A map-specific pet is rewarded in the chest once wave 14 is completed. The Giraffe on a Treadmill pet is rewarded in the chest after finishing wave 25.
Bosses have been added at the end of wave 25 in all boss maps Alchemical Lab, The Throne Room, The Summit and The Keep
Once you defeated a boss in Survival Nightmare or Massacre difficulty you unlock the Bonus wave of said boss on all maps which are below the Bossmaps so for example if you beat the Demonlord in alch lab on wave 25 in nightmare you can choose the Demonlord bonus wave in all act 1 maps but not act 2, 3 and 4
The bonus wave will spawn enemies with the HP and damage from the boss wave you choose but you will only have to fight another boss if you play a boss map itself the bonuswave doesn't add the boss itself to other maps