to start with whats last

some good introductory corals are zooanthids and mushrooms...but remember, even they will need significant lighting. Sun Polyps, on the other hand, require no lighting, but do require feeding...so if you're lights aren't up to par that might be an option to consider.
yellow goby: there are a couple yellow gobies...the "yellow clown goby" (gobiodon okinawae) and the "yellow watchman goby" (cryptocentrus cinctus). I think either would be suitable, though the clown goby is smaller which might be better in a 12g
catalina goby: though suitable, perhaps not the best choice because they come from a cooler water environment (Catalina

) and are not truly tropical
common clown: I think a pair of percs would make a nice display in this size tank
maroon clown: imo the maroon grows too large to be kept in a 12g
bicolor blenny: another interesting choice, pretty active little guys though i have heard rumor that they get kind of mean...esp. with other bottom dwellers
purple firefish: i think this is the best choice! hardy, colorful, and active. i think if you could get a m/f pair that would be superb! another option might be the fire dartfish (nemateleotris magnifica)
royal gramma: i dont think this fish would be a problem in your tank...another fun choice.
pyjama wrasse: not sure what this fish is. i am going to assume you mean pyjama cardinalfish and go form there. I think this fish might feel a bit cramped in a 12g...but it might be ok depending on how much LR you have and whatnot
as far as combinations, i think that any
one of these fish would be great for your tank, or pairs where i suggested. perhaps, you could keep the clown goby with one of the other top/mid level swimmers, but its a really small area for any SW fish...hope that helps some
K