This spell costs less to cast for each different mana value among cards in your graveyard.
Whenever you discard a nonland card, you may cast it from your graveyard.
Oskar is a discard-payoff engine: load your graveyard with varied mana values to cheapen him, then turn every discard into a free cast from the yard. You fill the bin with cantrips, wheels, and rummaging effects, then chain cheap-to-recast value spells and bombs you discarded.
Turns discard 'downside' into pure card advantage and free casts
Often costs only or less to recast after a single board wipe of value
Excellent with reanimator and cheap-to-recast spell engines
Free, untap-driven looting that turns your graveyard into an engine alongside Oskar.
Add discard outlets that don't cost mana and graveyard-fuel like Frantic Search, Cathartic Reunion, and Tortured Existence. Lean into a tight reanimator or storm-style combo line with Underworld Breach, and run protection plus graveyard recursion to fight hate. Tune your curve to maximize distinct mana values so Oskar consistently costs near zero.