These can be extremely hard to pull off in most decks, as they tend to raise alarms for opponents when played
Some creatures are bound to the cold by Rimewind magic
Intrepid Adversary Intrepid Adversary provides a mana sink and a power boost to aggressive creature decks
It can send a Umi to the GY and Special Summon 1 WATER monster from your hand
The existing mana constraints checklist for those wondering: Allied pairs can support doubles in both colors due to cycling lands and Ixalan checkland reprints (U/W Gift, U/B Control), no-one-drops allied shards work due to an excess of both of those (Grixis Energy and Naya Monsters), and wedges work best with one-drops in the shared enemy color (Llanowar Elves in Sultai) or as allied pairs splashing the third for some whammy (Brad Nelsons Sultai Midrange)
One bridge is being blocked by an NPC, who claims that they are testing "to see how many people it can hold at one time" Naturally, the test concludes at the precise moment you beat the champion