Endless Mode

Endless Mode is one of the 4 modes to select in DtK:R. 
As the name states, it is an endless mode. It goes by Tiers rather than Waves, and Enemies get progressively stronger with each Tier.
The Enemy Health formula is: \Delta \text{Enemy Health} = \left( \frac{T}{2} \times \text{BaseHP} \right), where T is the Tier number.
Bosses have an additional Health scale of 20% per Player.