Regeneration is a buff that heals the character's health at the end of the turn. "End of turn" will not be evaluated if you win the battle - if you kill the final enemy, regen will not trigger.
Regeneration works similar to poison, the number represents the amount it will heal and the turns left, after each turn, the number decreases by one. When the number reaches 0, regeneration wears off. Because of the way it works, multiple Regen Potions stack quadratically: taking one potion can restore 15 HP over 5 turns, but taking two in succession can restore more than that in the first two turns.
Sources of Regeneration:
- Regeneration Potion: Gives the player 5 regeneration
Not to be confused with the Awakened One's regeneration ability which heals at a flat rate of 10 health each turn, neither stacking nor decaying.