As Chrollo can only use 2 abilities at once (besides Bandit's Secret + Bookmark), God's Alibi (Meleoron) + Scream (Knov) would be the perfect deal to make him invincible IMO... there's nothing I can think of to counter that combination (Ripper Cyclotron could also replace Scream). Plus, he would've access to many other broken abilities, the possible combinations would be insane: Cat's Name, Parallel Future, Spiritual Message, Spatial Teleportation, Predator, Wink Blue, Cross Game, Countdown, etc.