Have 14 Green gems, power cost is 10. Enemy has 8 Strike and Protect Tiles on the board. Facing Venom (1*), Daken (2*), and Bullseye (2*) with The Hood (Classic, Intimidation) as the support card. No ability for countdowns on the board. Us the Power, enemy Strike and Protect tiles reduced by 1. I would expect 2 to be missing, as the power reduces the pool by 10 and as my pool didn’t increase afterward I didn’t make a green match that would increase the enemy strike tiles.
3*Groot’s green destroys the tiles at random. It doesn’t always destroy special tiles, only make the special tiles a possible choice. (Unlike some other powers that say "destroy random basic tiles, which, in this case, the special tiles will never be destroyed directly by the power.)
To be clear, Groot will destroy the 4/8 tiles in the middle of the board regardless of what type they are. (Ok, except fortified and locked tiles, which he’ll merely unlock).
The bonus destroyed tiles per 2 Green AP (that’s one tile per 2 Green AP total, not per 2 Green AP over 10) are chosen randomly from the remaining 56/60 tiles, and can (not guaranteed) include non-basic tiles as described in the level of the power.
So in your example, you have 14 Green AP. The power will destroy the 4 tiles in the center of the board (assuming you don’t have 5 covers in the power, if you do, it’ll destroy 8) plus an additional 7 random tiles which could be either basic tiles, enemy protect tiles, or enemy strike tiles, for a total of 11 (or 15) tiles destroyed. The power costs 10 Green AP, so after you use it you’ll have 4 left unless you got a green match in a cascade from the destroyed tiles or something.
Thanks for the clarification.