Whatever you put in there, have little expectation of it to live.
Personally I'd try small damsels first. shellfish are primary targets of mantis, fish tend to stay up higher, and be faster which mantis won't waste energy chasing over the snail next door. Shrimp would have no chance.
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I used to have two o. scyllarus at the same time. One was a full grown giant, the other was a small 3" long baby, both opposite sides of the room.
The full grown giant co-existed the entire time I had it (about a year) with a N. Oxyodo damsel sleeping literally in his burrow, which is testament to the balls on these fish (two domino damsels 'disappeared' early on though).
The other one would kill rocks that twitched from the filter current and my premium rock which came with a ton of things living on it (including an N. wennerae as a bonus for my sump!) turned into a desolate base one. When I eventually moved her up into the other one's tank, I honored the damsel for surviving the first mantis by donating it elsewhere instead of trying round 2, knowing this one wasn't having it.
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Speaking of that hitchhiking N. wennerae, that was removed before the o. scyllarus went in, obviously it didn't go to town on the rock, and it didn't kill the two emerald crabs I had in the tank for a few days until I moved them into the reef tank.
On the other coinflip side... the store had another N. Wennerae they found that actually broke out of the critter container, and went on a killing spree in their emerald crab tank.