Epic Resilience

Introduced in Update 14, monsters in Epic Elite difficulty receive a bonus to their saving throws versus magic depending on their health.
 * +6 at full health
 * +4 when slightly hurt
 * +2 between 50% and 75% health
 * no bonus below 50%

There's a similar but smaller bonus on Epic Hard.

The Epic Resilience mechanic is not used in The Temple of Elemental Evil.