Eh...
Couldn't go through the 2nd level. :(
This barrier with spikes above it got me! Great game, though.
It would be cool if you added more "auras"(shields), like yellow and green, and a secret powerful black aura.
I've founed some kinda effective tactics:
1) Use the same aura your enemy uses. You will do less damage to it, but it won't do any damage to you at all.
2) When you feel you are low on life, and going to lose, use the "instant kill" option. You will start from the last checkpoint, not losing 1 player.