Ooohh!!
I got tons of ideas,
But all of them depend on your friend's preference, so he could do:
a mantis shrimp (IMO I find them scary)
he could do a shamed face crab, AWESOME CRAB!!!
Harlequin shrimps
some type of lobster
sexy shrimps
decorator crab
young horseshore crab, it would get too big though
Myabe a small octopus (anyone know if he could do that?, I'm not sure if there are any dwarf species)
I can only see some type of clown goby as being a fish to keep, a yellow clown would be good with the shrooms.
hope this helped