Born in the Boughs --
1G
Instant {U}
Creatures you control entering the battlefield this turn enter with an additional reach counter on them.
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Born in the Billows --
2U
Instant {U}
Creatures you control entering the battlefield this turn enter with an additional flying counter on them.
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Born in the Barracks --
3W
Instant {U}
Creatures you control entering the battlefield this turn enter with an additional first strike counter on them.
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I could possibly extend this to a full five-color cycle, but I'm partial (ahem) to partial cycles. The wording seems slightly off, but I really don't want it to set up a triggered ability.
There's an additional balance between cost and reward; too expensive, and you can't combo it with other creatures. This sort of ability does go really well with tokens, especially things like
Avenger of Zendikar and others that create multiple tokens at once.
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Subsumed by Fungus --
WBG
Enchantment - Aura
Enchant creature
2: Remove a counter from enchanted creature.
3: Add a counter of a type already on enchanted creature to enchanted creature.
Utility enchantment for a counter-based set; there are a lot of variabilities at play.
Either ability could open up to be able to be activated by any player. The costs to activate could change to hybrid mana (WG to add a counter, WB to remove). Changing the activation costs, though, limits whether other players are able to activate the abilities.
Plus: What if it could copy counters (to, or from other counters), or if instead of removing counters, moved them to other creatures.... What if it could enchant things other than creatures?
Since it's meant to represent both positive and negative counters, is "subsumed by fungus" really the best flavor?
Hmmmm.