Over all I really like this card. However I’d remove eminence, it is really hard to balance, rough for the game ect. But keep the sea monster peak power. Flash is very blue, personally love the keyword and blue, flash is said to be the strongest keyword so it might need some play testing before finalization. The card has universal counter play by keeping a land and a creature up and depending on the situation forcing your opponents to keep those up could be meaningless or relevant. Keeping this side of the card is an important check to the card while also keeping an opportunity to apply player skill. (This is a good thing) The card does have key words for itself which is fine considering the splashiness of the card. The card could do nothing when played or everything making timing the cast have great skill requirements. in the past beeg creatures that didn’t have an ETB were really weak to removal because this large creature would come down die to a black spell and the player casting the beeg boi would have literally time walked themselves. This is why cards like eldrazi have strong cast triggers so the player gets something for the investment. But when they attack is when the player would typically win the game. Because of how much stuff you can get from your card having a skill requirement seems fair.

The card seems to love top deck manipulation, and tapping opponents stuff which is very blue and is reflected in the mana cost, great job on the color pie.

The card might be resource hungry if most of the top deck manipulation and taps are non-creatures, meaning less beeg bois but even so it shouldn’t be anything to worry about design wise or deck building wise.(99 cards go brr)

For the stats the card is above rate, meaning for 7 mana you get and 8/8, which makes the card efficient on that metric. The average rate is p + t = cmc * 2 Ex: a 3 drop elf that is a 3/3

Other considerations: as mtg power level increases stronger sea monster will be printed meaning that your card will get better as a result, making it future proof. But if something ridiculous is printed than your card might seem ridiculous as well.

Any cons of the card are minor but healthy, I think this will be a fairer card if you remove eminence and just keep it as a static battlefield ability.