I've had this question on my mind for a while now. Only until now when I remembered it digging through old codes back from 09'-10'. But are .mng files still accepted as shields, swords, and heads? Because back when I first started playing I did remember using some .mng file codes.

Some examples:

bomb-shield.mng
blueani-shield.mng
bluefire-shield.mng
bouncingball-shield.mng
dark-shield.mng
darkman-shield.mng

And my personal favorite, faceani2-shield.mng

Those are just a few examples that may bring you back to nostalgic times. All of them are also useable in .gif I believe. Just out of curiosity I wanted to know if you're still allowed to upload in .mng and if not why it isn't around anymore.  

.mng still works if the server allows it.  

The uploading website doesn't accept .mng files and it's a good thing because they are often 5x the filesize of gifs and don't provide any extra benefit.  

Rufus, you apparently thought about this almost a year ago! :P

MNG files are lossless files, which causes them to be larger, yet carry more data. This avoids image/color inaccuracy, although you really can't tell the difference. Its similar to the difference between WAV and MP3 files for audio... Also, GIF files are a bit lossy, but are supported in all web browsers. Certain browsers only partially support MNG files anyway, so its probably best that they aren't accepted.