Way too buggy. For missions depending on collecting debris, if you blow up whatever drops the debris then leave the system and come back, it's gone and you're screwed.
To kill a guardian, make sure you have enough mana in your pool for it to go around twice. Use lots of low level blue/cyan to keep it slowed/stunned, and IMO high level yellows, or duals with strong yellow component. Triple damage rocks!
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 "GemCraft chapter 0"){kind=icon}
 "Mirrored Maze 3"){kind=icon}