At the start, swim high up, it is stuck to the ceiling.
At the upper level of the area, where the rooms are, go to the left and shoot the plants with Silver Lego Blowup (e.g. Ironman). Put together a Portal Pad and use Portal Create (e.g. Doctor Strange) to go through. The Minikit is inside this room.
Character in Peril (Stan Lee)
Destroy everything in this room (Minikit 2 room). Then put together a grapple with the pieces. Use Single Rope Pull (e.g. Ms. Marvel) to the left and pull down a bed to save him.
In the same room, use Vent Travel (e.g. Ms. Marvel) on the vent. Then use Dig on the dig site (e.g. Rocket) to get the Minikit
In the same room, the one with the animals, use Electricity on the Electricity Pad (e.g. Thor)
Go out again. Find and shoot 5 Silver Statues with Silver Lego Blowup (e.g. Ironman)
1 - Starting area, upper level
2 - Starting area, lower level
3 - In the corridor, before swimming through the shark mouth.
4 +5 - Boss fight area
Token: Blue Marvel
At the starting area, lower level, destroy everything near a big rock on the floor. With the parts, buy a Gravity Mine point and use it (Star-Lord)
In the next big room, where you take control over the fish in the story, go bite the chest to the left first.
Once you left this big room, in the water, swim back. On top of the corridor roof, there is a pile of rocks that you can move with Telekinesis (e.g. Doctor Strange)
Close to the shark mouth, there is a little cave entrance covered in vines. Use Vine Cut (e.g. Black Panther)
From there, swim up, before you go through the shark mouth. The Minikit is hidden behind a stone.
Now swim down again, through the shark mouth and to the left. There is a tracking site. Use it (e.g. Black Panther) and dig up Minikit pieces. Just put them together.