Board Thread:M.U.G.E.N Help/@comment-27010437-20150923002406/@comment-5289928-20150923104216

Most of these are achieved by agreeing to use certain custom animation numbers (usually in the upper 5000s and 7000s range) as extra 'standards' for special hit animations, so when people code their eletric/fire/midnight bliss/etc moves they can check if the opponent has this anim and change to it knowing it will probably look right in 99% of cases.

This is a list of the most common special animations and examples of characters that can cause them:

http://mugenguild.com/forum/topics/optional-animation-standards-138791.0.html

An even more comprehensive (but in Japanese) list of animations some characters use for special graphics can be found at http://shakesdream.web.fc2.com/SpecialStatus_top.html