Geological Appraiser

Discover was built to reward casting a spell rather than cheating it out, and this is the payload card the mechanic was aimed at: a four-mana body that, when cast, digs through your library and either slams down a free spell of mana value 3 or less or tucks it into your hand. The clause "if you cast it" carries the whole restriction. It shuts off the flicker loops and reanimation tricks that would otherwise turn a single body into a repeatable engine, forcing the trigger to come from actually casting it at least once. The trouble is that "a nonland card of low enough cost, cast for free" is a category wide enough to include other cards that themselves produce a free spell, and combo players found the seam almost immediately: chain enough cheap bodies that each discover into another, thread in cost reducers to keep the cascade rolling, and the whole deck empties out of your library in a single turn. That fragility of the constraint is why the card mattered beyond its rate. Discover 3 attached to a fair creature is a value bump; discover 3 attached to a pool that includes more discover became a one-turn combo kill that earned it a ban. The 3/2 stapled to it is almost incidental: the body exists so the card reads as a creature you might play on curve, while the exile-and-cast clause is the part that priced every other three-drop against what it could conjure for free.