Im playing it right now and wonder if its possible to max out all arrows?
you can replay levels once you beat it.
Now I have to say,
Arrows:
Fire: causes damage over time, burning effects, enemies still can shoot stuff at you.
Ice: freezes enemies and the start to fall, they can still shoot stuff however.
Lightning: lightning arcs through towards enemies when they are close enough.
Piercing: will go through multiple enemies, until the arrow is stuck fast into the hull of something.
Explosion: massive damage.
Homing: makes the missiles gravitate towards enemies.
Traitor: turns enemies against themselves, they have a purple halo around them, they will generally float around doing nothing though.
Teleport: will teleport enemies to the off of the screen, unless the arrow kills them.
Lead: a stronger arrow.
Gravity: when hit will make enemies stick with each other and fall towards the ground.
Helium: will make enemies lighter and allow you to do more damage.
Time: will freeze enemies completely.
thats about it.
Fire+Ice = most usless btw... most useless...