KiraVaran
I think maybe a beastial battle ring (for any class). You would be able to use certain abililties of a particular animal. For example:
Wolven Ring
Level 1 - Bite (use fangs to attack your opponent)
Level 2 - Tear (a stronger Bite, tearing at your opponents throat)
Level 3 - Howl (making a certain monster afraid, ie he looses a certain number of turns to attack)
Level 4 - Pack Mentality (a wolf joins you in the fight for a certain number of turns)
Snake Ring
Lvl 1 - Bite (do damage)
Lvl 2 - Scales (scales add extra protection)
Lvl 3 - Spit Venom (slightly weaken your opponent)
Lvl 4 - Venomous Bite (do some damage and weaken opponent)
This could be used with all sorts of animals. A turtle ring could let you hide in a shell, a horse ring could let you move faster, and cat ring could let you pounce an opponent from behind.
1. Your aware that there won't be actual classes, just ring sets that give bonuses, right?
2. The MMO isn't turn based so you might need to tweak your ideas abit.