If I have a Double Colorless Energy attached to Tangrowth, will its "Grind" attack do an extra 20 or 40 damage for that energy card?
It will do an extra 40 damage. Grind looks at the total amount of energy attached, not energy cards.
Grind

Other known variants



+20
GrindDoes 10 damage times the amount of Energy attached to Lapras.


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If I have a Double Colorless Energy attached to Tangrowth, will its "Grind" attack do an extra 20 or 40 damage for that energy card?
It will do an extra 40 damage. Grind looks at the total amount of energy attached, not energy cards.