My opponent has Grafdigger's cage in play. I cast Replenish which brings back Opalescence and Pandemonium. Will Grafdiggers cage stop Pandemonium from entering or not? I'm guessing not since it needs to be on the board to be active.
No. For Grafdigger's Cage, what matters is whether Pandemonium is a creature card in the graveyard (C.R. 109.2a), not whether it will be a creature on the battlefield.
MODERN:
RG Shamanism RG
WUG Blades of the Avatars WUG
LEGACY:
WUBRG Cascabalance WUBRG
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"Some say the clockwork doesn't speak... I say they are deaf to it's voice." -Daeren, Artificer Druid.
Archester Revival (Custom Steampunk set)