Below is official Champion Spotlight which for some reason they failed to update yet:

Now, in-game it says:
"When below 30% Health, each Persistent Soul Charge is consumed, Regenerating 10 Health per charge. Mephisto does not take damage while consuming his Persistent Soul Charges through this ability."
So here are a couple of HUGE issues with this dear Kabam:
1) People spent their 5 star shards, catalysts, gold to get Mephisto and rank him up. Now these are worthless or MUCH less worthy.
2) People spent revives, health potions to defeat Mephisto in his old form in Blades quest. He would be much easier with the nerf
3) People spent hundreds, thousands of coins for a chance to get him using his featured. I am one of them
At this point Kabam HAS to:
1) Issue 5 star shards and rank down tickets to those who spent their shards and ranked up Mephisto
2) Issue revives, health potions to those who fought Mephisto in Blades quest when the was overpowered
3) Issue coin refunds to those who spent coins to get Mephisto using the featured crystal
Do this please.