seidon looks a bit strong, it is a better cheaper dream halls or a blue recycling. I dont know how strong that would be, but it looks really good
Yeah, that's why I made him cost 2

, and start with only 2.
I mean, blues non-aligned colors can both reasonably deal a helluva lot more damage than 3 by turn 4 - and the dream halls ability is neutered by the planeswalkers' inherent "sorceryesque" abilities.
What? I don't follow you at all. Even if they kill the Walker in response, you still get the Dream Halls ability for that turn, and it isn't very hard to just win on the turn you play him, so they can't even kill him via the attack step.
This is very, very broken. Really, all three abilities are close to the kinds of things I would expect to see as the "big" ability on a planeswalker.
For that matter, none of these abilities seem very connected to an ocean god. They're just hilariously powerful - one giving you tons of extra cards, and the other giving you tons of extra mana (basically turning every blue card and island into a Blacker Lotus). I can't imagine EVER using the third ability when I have drawback-less Recycle and hyper-powered Dream Halls (I can pitch lands omg?!) to choose from. The abilities also don't really feed into each other very well, unless they're feeding into each other WAY TOO well and you're drawing 8 cards on odd turns and playing 8 spells on even turns.
Probably a better set of abilities, which is more in tune with him flavor-wise, would be:

<3>
<+1>: Until the beginning of your next upkeep, target land becomes a basic Island.
<+1>: Target creature gains islandwalk.
(This effect does not end at end of turn.)<-3>: Until end of turn, whenever you tap an island for mana, add

to your mana pool.
He can slowly make your entire team unblockable, mess with opponent's mana, and then High Tide. I tried to cost these low enough that you wouldn't just cash him in, but rather get him to 4 counters to be able to reuse him. All three abilities are clearly related to having lots of water around, as befits a God of Waves.
(The first ability can also help against Blood Moon, for whatever that's worth.)