For Xerneas' "Power Creation" attack, do I need to heal all damage from Xerneas in order for the attack to do +80 more damage, or can I just heal some damage in order to get the benefit?
As long as you have healed any damage from Xerneas this turn, you get the bonus damage effect.
Source: BREAKthrough FAQ (2015-11-19), TPCi Rules Team (2015-11-19)

Relevant cards

Note: All applicable cards may not be listed below.
XY8_107