A solution to your battlesphere dilemma that i just saw, use the splinter twin combo to create infinite galvanizers, then tap them all to Battlesphere, that way you can deal infinite damage with the battlesphere...
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I agree with Ghost1599, You can't split the stack when tapping myrs for the battlesphere. And yes, it is very vulnerable. What happens if your opponent pulls a safepassage when you try to attack with your infinite myr's? Or he has a palace gaurd (add protection from colorless, no damage to palace gaurd when blocking all of your myrs...) Just some things to think about..