the one ring mtg card kingdom From Magic: Gathering Pulled You may play 1 level 5 or lower Digimon card with the [ADVENTURE] trait from your hand without paying the cost Our Courage United (ST20-14) -

Contents: 36 Outlaws of Thunder Junction Play Boosters

For three mana, you decide how much life to pay and shrink every creature accordingly

Adagia, Windswept Bastion Applied Geometry Artificer Class Ashling's Command Brigid's Command Cabaretti Confluence Cackling Counterpart Caretaker's Talent Chandra, Flameshaper City of Death Cogwork Assembler Croaking Counterpart Dance of Many Dino DNA Donatello, Gadget Master Dutiful Replicator Echo Storm Electroduplicate Elvish Hydromancer Ember Island Production Esika's Chariot Esper Terra Fated Infatuation Feldon of the Third Path Flash Photography Ghired, Mirror of the Wilds Grub's Command Hazel of the Rootbloom Heat Shimmer Ignite the Cloneforge

And in the case of Bosh, his cost increases the damage he does, so there's some built-in synergy there

Not sure if its too narrow, but Ive liked it so far

perhaps too many options