I could see Grim Discovery + Prismatic Vistas being worth it if Bx Domain/Landfall is a thing in your cube.
More seriously... Regrowth effects kinda suck unless your format has ways to abuse them. Like, theoretically there's a format where casting Regrowth to get back your Brushwagg is a good play¹, but it really wants to be looping Shigeki or "protecting" a key combo piece.
¹ This is theoretical because it assumes that there's a format where villain can put your Brushwagg into your graveyard while you're still alive.
EDIT: The environment that Grim Discovery wants to be in is one that's full of channeling/cycling. Like, Grim Discovery in a deck with Drake Haven and a bunch of cycling creatures/lands sounds like it could be grindy fun.
More seriously... Regrowth effects kinda suck unless your format has ways to abuse them. Like, theoretically there's a format where casting Regrowth to get back your Brushwagg is a good play¹, but it really wants to be looping Shigeki or "protecting" a key combo piece.
¹ This is theoretical because it assumes that there's a format where villain can put your Brushwagg into your graveyard while you're still alive.
EDIT: The environment that Grim Discovery wants to be in is one that's full of channeling/cycling. Like, Grim Discovery in a deck with Drake Haven and a bunch of cycling creatures/lands sounds like it could be grindy fun.
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