Whenever Caparocti Sunborn attacks, you may tap two untapped artifacts and/or creatures you control. If you do, discover 3. (Exile cards from the top of your library until you exile a nonland card with mana value 3 or less. Cast it without paying its mana cost or put it into your hand. Put the rest on the bottom in a random order.)
Caparocti is an attack-trigger value engine: swing in, tap two artifacts and/or creatures, and Discover 3 to cheap free spells onto the battlefield or into hand. You build a low-curve Boros board full of cheap artifacts and creatures (especially mana rocks and tokens) so tapping the cost is painless, then chain Discover hits into more aggression and value while crashing in for damage.
Free card and mana advantage every combat with a low-curve deck
Mana rocks and Treasure tokens double as both ramp and free fuel for the tap cost
Aggressive Boros body that pressures life totals while generating value
Discover can flip into instants/sorceries for surprise interaction or burst
Reliant on connecting in combat; removal or chump blockers shut off the engine
Caparocti must attack, exposing him to combat tricks and deathtouch
Discover whiffs less than other tutors but is variance-dependent at MV 3 or less
Boros lacks card draw and recursion outside the engine, so disruption hurts
Floods you with Treasure tokens to tap each combat without sacrificing real resources.
Lower your curve aggressively so every Discover 3 hits something impactful, and lean into Treasure and token producers (Dockside Extortionist, Smothering Tithe, Goldspan Dragon) to make the tap cost free. Add evasion and combat protection like Reconnaissance and equipment so Caparocti reliably connects, and tighten removal to cheap, flexible instants that Discover can also flip into.