Before you do, you should know that the game treats any HP gain as healing.
You'll have to lock the ability to Holy Light / Angel Heal rather than healing.
Also +2 stacking is uber compared to +1 stacking.
Do you mean Blessing, Chaos Power, Growth, etc.? The card text won't have to be clarified, though (that would be one LONG card text!). I think it's clear enough only actual
healing spells and abilities are intended to work with this effect. What did you mean for me to change, exactly?
I am aware +2 is much more powerful than +1. Do you believe +2 would be overpowered? Say you have four of these out and a guardian angel with armagio companion. That's 23

and 5

to set up, and the armagio will gain 8 attack per turn at the cost of 1

, versus 4 attack for the same.
EDIT: Running a simulation here, best case scenario with Mark of Gravity/Armagio:
Turn 1 - draw Light Tower x5, Crusade x2, end at 10

/1

Turn 2 - draw Crusade, end at 15

/2

Turn 3 - draw Crusade, end at 20

/3

Turn 4 - draw Guardian Angel, end at 25

/4

Turn 5 - draw Armagio, end at 30

/5

Turn 6 - draw Guardian Angel; play Armagio, Guardian Angel x2, Crusade x4; cumulative damage = 3
Turn 7 - draw and play Guardian Angel, heal Armagio twice (now 17 attack), cumulative damage = 23
Turn 8 - draw and play Guardian Angel, heal Armagio thrice (now 41 attack), cumulative damage = 68
Turn 9 - total damage will be over 100.
Compare this to ideal shrieker rush:
Turn 1 - draw Stone Tower x5, Elite Graboid, Long Sword, play Elite Graboid and Long Sword, end at 6

/1

, cumulative damage = 8
Turn 2 - draw and play Elite Graboid, evolve a Graboid, end at 8

/1

, cumulative damage = 26
Turn 3 - draw and play Elite Shrieker, evolve a Graboid, end at 5

/1

, cumulative damage = 62
Turn 4 - draw and play Elite Graboid, end at 7

/2

, cumulative damage = 100 (!!)
Obviously the main concern is what a superbuffed critter would do to a stall deck - but this strat probably can't outrush most rush decks. In the above Crusade deck simulation I did hold back on the combo until it could come out whole, it's a couple turns faster if you play things asap.