new mantis tank... roommate suggestions!!!!!!!!

[fiorano]

so i am upgrading my mantis tank from a 15 gallon to a 29 gallon.since there is all this extra space now i was thinking of adding something else to the tank as well. i was thinking maybe a dwarf lionfish but though him and the mantis might kill one another ... g smithii mantis. sooo any insight on that idea would be awesome, so would other suggestions as well thanks!!!!!