Back with some instance trouble, I just don't seem to grasp it ....
https://dl.dropboxusercontent.com/u/98471899/Scirra/testAI.capx
I tried to make some basic AI here and it works with one instance but if you duplicate the soldier it will mess up things. Not sure about the "For Each" event here, it doesn't seem to work with or without it....
And press Z will create a grenade that should land on the solid block, it works most of the time but sometimes it falls through the block if you keep pressing Z enough times.