Svyelun has indestructible as long as you control at least two other Merfolk.
Whenever Svyelun attacks, draw a card.
Other Merfolk you control have ward . (Whenever another Merfolk you control becomes the target of a spell or ability an opponent controls, counter it unless that player pays .)
Assemble a wide, evasive Merfolk board and pressure opponents with repeated unblockable attacks while Svyelun refills your hand each combat. With two other Merfolk on board she's indestructible, so she snowballs card advantage and you close games with islandwalk/unblockable beatdown backed by counterspells.
Built-in card advantage every combat keeps your hand stocked
Becomes indestructible trivially in a tribal shell
Ward protects your whole team from targeted removal
Mono-blue gives access to the best counterspells and tempo tools
Cheap 3-mana commander that recurs efficiently
Mono-blue lacks good board wipes and spot removal
Vulnerable to sweepers that ignore indestructible (bounce, edicts, -X/-X)
Legendary Creature — Merfolk God
. (Whenever another Merfolk you control becomes the target of a spell or ability an opponent controls, counter it unless that player pays