Type BOOGIE, STOMACH, GUT, BELLY, VORE, LEGS, BULGE, LATEX, MUSIC, VOICE, SIZE, SHORT, DANCING, TOBY, NIGEL, or THORNBERRY for Nigel.

Other commands, grouped together for what they do:
1. FUCK, SHIT, PISS, ASS, CUNT, DICK, COCK
2. MIDNA, TRISTANA
3. MELOME
4. FREAKAZOID, UNDYNE
5. PUPSPIDER, MUFFET, SPIDER, MULTIPLE, CHUCK NORRIS
6. SONG, DRAGONFORCE
7. TEM
8. SONIC, SANIC
9. (Typing anything else)
10. FUCK YOU

Those commands work for the one where Muffet has six arms.