Ward—Waterbend . (Whenever this creature becomes the target of a spell or ability an opponent controls, counter it unless that player pays . They can tap their artifacts and creatures to help. Each one pays for .)
Whenever an opponent draws their second card each turn, you draw two cards.
Cast The Unagi at instant speed with mana up, then sit behind counterspells while opponents do the work of drawing you cards. Every time an opponent draws their second card in a turn, you draw two—so you fuel symmetrical or forced-draw effects, then convert your massive hand into countermagic, card-advantage engines, and ultimately a blue wincon.
Generates enormous, repeatable card advantage off a single trigger that any extra-draw effect (yours or theirs) can exploit.
Ward—Waterbend makes the commander very hard to remove or tuck, protecting your engine.
Flash lets you deploy on an opponent's end step or in response to removal, dodging sorcery-speed sweepers.
Mono-blue gives access to the best counterspells, card filtering, and tutors to assemble a finish.
Mono-color means no access to efficient creature removal, ramp diversity, or recursion outside blue.
The draw trigger only fires on an opponent's SECOND draw each turn, so against draw-light tables it can sit idle.
Board wipes that hit nontargeted (Toxic Deluge, edicts, sacrifice) ignore Ward entirely.
Relatively slow clock—needs a dedicated wincon since the card draw alone doesn't end games.
Legendary Creature — Serpent
. (Whenever this creature becomes the target of a spell or ability an opponent controls, counter it unless that player pays 
.)