Mantis Shrimp can be rather annoying, and deal a sizable amount of damage - this is why I went to get the Jelly Costume first, for the passive health regen.
When Mantis Shrimp drops a volley of bombs, grab one with your Bind Song - switch to Nature Form, charge a shot and launch it at him. The stalk sprout will knock him off the ceiling, into the bubble just below. Use the Bind Song to drop the bomb next to him - when it explodes, it will harm Mantis Shrimp. Do this 3 times, and he goes down.
A risky (but nonetheless feasible) strategy would be to "kamikaze" into a bomb to force it to explode near Mantis Shrimp - he'll still take damage from it, but so will you.
Defeating Mantis Shrimp rewards you with a Verse Egg.
Steam Achievement: Boom Shrimp - Defeat the Mantis Shrimp.
Disclaimer: I do not own, or claim to own, any part of the displayed content - the art, music, etc...was all created by, and is owned/copyrighted by, the independent developers over at Bit Blot - the creators of Aquaria. I have no affiliation/association, or claim to have any affiliation/association with BitBlot. I am nothing more than a customer who purchased Aquaria on Steam, played it, loved it, enjoyed it, and wanted to post a play-though for Aquaria.