You'll want to use containers for this I think. Put all grass tiles into a container object. Pick one grass tile, all tiles in the bush are picked. Destroy one grass tile, all tiles in the bush are destroyed. Set the opacity of one tile, all tiles in the bush change opacity. Not sure why you don't just have one bush object though, seems like it would be easier. If you have to make the bush from 5 grass tiles then containers are the way.