Regeneration is a hero healing buff.
While in the battle, you can tap and hold the Buff icon and read what it does.
This buff  can be applied by the following heroes:
  • Alyria (Ability 3)
  • Hardorc (Ability 3)
  • Tromgar (Ability 3)
  • Senjiel (Passive Ability and Ability 2, 3)
  • Faelia (Passive Ability)
  • Shao Lin (Ability 1)
  • Lake (Leadership Ability)
  • Renara (Passive Ability and Ability 1, 2, 3)
  • Rawley (Ability 2)
  • Cent & Turion (Ability 3)
  • Ambu & Lance (Passive Ability and Ability 2)
  • Drago & Nas (Ability 3)