You gotta have:
Level 8 Squire
Level 8 Chemist
Level 5 Geomancer
Level 5 Dragoon
Level 5 Summoner
Level 5 Orator

After meeting all those pre-requisites, you can become a mime. All that a Mime Does is copy the last skill used before his turn. For example: Black Mage uses Firaga 3 tiles in front of him. If the next one to take an action is the Mime, he/she'll use a Firaga 3 tiles in front of her, no matter what is his/her target. Beware of that.

If i were you i wouldnt be a mime at times they seem very useless i used to have a couoke but shortly after they kept hitting my people in front who were my allies and when i wanted them to actually copy the move they didn't -,-

I as well do not suggest a mime they are the most useless class(2nd is Onion Knight) mainly because when it copies it attacks nothing in front of it, as well half the time it kills your own people

Contact me at Bdogtitans64@yahooc.om for more questions ^_^ good Luck

Mimes r useful depening on the situation. using them with dancers/bards is an excellent example doubling any dance/song's effect, basicly. another is the summoner because summons dont hit ur team, unless ur trying to heal. the last i can think of is the arithmetician, which same as the dancer/bard combo lets u double the spell's power. so all in all a mime is basicly a double-cast modifier for ur team. hope this helps. >.<