If it’s your initial clear Doom or Clair destroy the cosmic path. For the Grandmaster anyone can do it but champions with high crit rates work best. I used Stark Enhanced and Stealth Suit Spidey. Professor X is a life saver for phase 3 reverse controls
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I had Doom & Claire for path. Colossus and Prof X for GM. Plus NF just for attack boost.
Colossus was my MVP against GM.