Well this one I actually thought up myself, actually It's very simple. Also you need PC for it. It's the same thing as data swapping except you have to have some sort of costume item (mandy belt, rabbit belt). All you have to do is find the model of the costume you have ( here
http://ffxi.killvoid.com/page.php?id=229 ) then data swap it with anything that you would like to turn yourself into. (dragon, goblin, taru!) Then just simply use your costume item and you will turn into that thing.
And if you don't know how to data swap I will explain here. You need the PC version of FFXI. First of all go to whereever you put the playonline folder then squareenix-ffxi- then either of the ROM 1, 2 or wherever the one you want to change is in. Let's say you want to change your moogle into a behemoth. Just go to where the moogle is (rom 1 folder 3, number 56) Then copy 56 and paste it into folder rom 1 naming it something to remind you what it is i.e. 3-56-moogle. Now find the behemoth file (rom1-folder 5- number 52) copy it and paste it into rom 1 and rename it 56. Now cut it and paste it into folder 3 and replace the old 56. Next time you log in, all moogle's will be a behemoth! and that's my guide