I got one of the Colossus Slabs early on after I upgraded my then newly level 20 sub. It's all Unkai parts now. The Shark parts are now on sub #2. I've gotten one of the slabs and one jelly minion in about 6 runs so far. Never got anything useful with Shark parts while leveling sub #1 so will likely swap out all the parts again when the second sub hits 20.