I'd want to be so big that the largest of whales seem no bigger than a dog in comparison. Then I can attempt to explore the oceans without fear that something big and scary is gonna devour me in a single bite.
Mmm probably explore a lot of places then I'd build myself a massive mansion and build anyone I care about a mansion too or y'know whatever they want to live in. Just build like my own little town and only allow certain people in it so it'd be like a game of sims or something I guess. Like I'd organise where houses went and decide who I wanted to let in and if someone was giving anyone in my town a hard time they can expect to be thrown to the bottom of the ocean or placed in a really really really high tree (or I could just squish them I'm not really picky about how they die). Then I'd go befriend a whale.