Primarily you gain it from a talent picked from the Level 5 row. Other ways you can get it:
Heroic Intervention trait on orange melee weapons. Note that this is kinda glitchy, the “staggering enemies who are about to backstab” triggers inconsistently.
Career skills of some characters like Mercenary’s Shout
Also some characters have talents that give temp health to the team in certain scenarios.
I don’t know about if the auras stack with inherent damage reduction or not. but I will tell you the auras are pitifully small you have to hug pretty close to someone to count on it.
Hmm, yeah I thought there would be more ways to gain temporary health, other than the lvl5 talent.
Because some heroes have two types of talents sharing the lvl5 tier.
one that says “you gain temporary health” and another that says “restores temporary health”.
But how do you restore what you cannot gain? XD
Thanks.