Multiple times now I have been in an arena battle where I have ended up losing because every time I attacked the enemy, they healed the damage while the attack was still going on. The first instance was a player named Zukkuss whose team was level 50 5* Zelotah lead, Hope, Thenasil, and level 60 6* Lightsworn, all max asceneded with a team power of 45850, compared to my team power of 68080. Eventually it got down to his Lightsworn and my Valkyrie, but as I was attacking him, his health would go up. Most recently, I fought a player named Jazon85, who's arena defense is a solo Atur, Level 60, max ascended, for a team power of 25016. I use Atur in arena myself, so I am aware that he heals when crit for the first time, and has a 2 turn cooldown, but his Atur healed after every hit I did to him, and the Atur ended up killing every one of my units (Battlesage lead, Valkyrie, Kallia, Atur). Both of those units were on Regeneration artifacts, so I am unsure if there is some form of mastery which causes this that I am unaware of, or if there is a glitch in the Regeneration artifact set, or if the 2 players are indeed hackers. There have been other instances of this heal while being attacked has happened, but I do not recall their names at this time.