Why don't you use Earth Pendulums in exchange for Towers, and change mark to Entropy?
Because the possibility of getting a first turn Supernova is simply something you cannot give up. Also, it would be 3 turns before you could use a Supernova which is a really, really bad thing for a PSNbow (or in this case a Speedbow). Sure, you can get Graboids out faster, but you won't even be able to evolve them until your third turn.