YES!
draw them in different outfits as long as they're still recognisable.
do joke drawings of them
draw them with other characters
angst
basically somewhat anything as long as it is SFW
NO.
any NSFW/fetish/suggestive artwork whatsoever. not only am i a minor but this also goes against my religion.
Shipping, unless said otherwise.
Gore, unless said otherwise.
Change the race, species or gender of the characters.
Toilet-related stuff [includes piss, scat, f*rting, etc]
Draw underage characters with purposely big breasts or large thighs [not in a digitigrade way]
Anything offensive [eg: racism, lgbtq discrimination, ableism, nazism, zionism, pedophilia, incest, etc…]