Whenever Rith deals combat damage to a player, you may pay . If you do, choose a color, then create a 1/1 green Saproling creature token for each permanent of that color.
Rith is a midrange tokens engine that flies in for combat damage, then pays to flood the board with Saprolings keyed off a color's permanents. You ramp into Rith on turns 4-5, connect, name the most common color in play (often green from your own tokens/mana dorks), and snowball into an overwhelming go-wide army. Convert that army into damage with anthems or a single explosive overrun.
Generates a huge, repeatable token swarm that scales with the board, including everyone's permanents
Naturally aligned with green's best ramp, white's anthems, and red's overruns
Flying body that dodges most ground blockers to reliably trigger its ability
Resilient to single-target removal since the value comes from each combat connection
Requires combat damage to a player, so it folds to fliers, deathtouch blockers, and Fog effects
Six-mana commander that does nothing the turn it lands unless it survives to attack
Token strategy is vulnerable to board wipes and sweepers like Blasphemous Act
No evasion granted to the army you build, so closing can stall against bigger boards
Costs an extra each trigger, taxing your mana every turn