His -5 gives you an emblem that makes it so you can tap your Mountains to deal one damage to any target
In fact, after all these years, I still keep my Seismitoad list from that period that helped me win a lot of games
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I tried building him Voltron, and while in theory Ragavan looked like a clear favorite to pull this off, in practice I noticed that I had precious few ways of giving him evasion which really hurts his viability and Mono Red gave precious few ways to ramp or draw without him

Amoeboid Changeling Avian Changeling Barkform Harvester Belonging Bloodline Pretender Cairn Wanderer Chameleon Colossus Changeling Berserker Changeling Hero Changeling Outcast Changeling Sentinel Changeling Titan Changeling Wayfinder Chitinous Graspling Chomping Changeling Feisty Spikeling Fire-Belly Changeling Flock Impostor Game-Trail Changeling Gangly Stompling Ghostly Changeling Gladewalker Ritualist Graveshifter Guardian Gladewalker Impostor of the Sixth Pride Irregular Cohort Littjara Glade-Warden Littjara Kinseekers Masked Vandal Mirror Entity Mischievous Sneakling Mistwalker Moonglove Changeling Moritte of the Frost Morophon, the Boundless Mothdust Changeling Mutable Explorer Omni-Changeling Orvar, the All-Form Prideful Feastling Realmwalker Rooftop Percher Shapesharer Sizzling Changeling Skeletal Changeling Taurean Mauler Three Tree Mascot Turtleshell Changeling Universal Automaton Unsettled Mariner Valiant Changeling Venomous Changeling War-Spike Changeling Webweaver Changeling Woodland Changeling

Focusing on frogs cuts into the number of slots you have for enchantments, but you get to run bigger threats like Yargle and Multani to have more and better targets for your limited auras