BUR #24196 has been rejected.
create implication pegasus -> mythological_equine
create implication unicorn -> mythological_equine
create implication winged_unicorn -> mythological_equine
create implication mythological_equine -> equine
create implication horse -> equine
create implication donkey -> equine
create implication pony_(animal) -> equine
create implication zebra -> equine
Collecting all of these.
As I'm not too into the terminology I wasn't too sure whether to use equine or equid. Looking up the difference leads to a marketing site saying equine is only for horses while the wikipedia page points to "equine" being the proper name for everything in equus https://en.wikipedia.org/wiki/Equus_(genus) including zebras and asses and a dictionary presents it as being mostly used for horses but also including donkeys/asses and zebras.
I decided against implying unicorn, pegasus etc to horse as people looking up the tag might want actual irl horses and people might draw zebra unicorns and such. Either implying them to "equine" or going with the "mythological equine" approach of e621 seems the best solution.
Also this should include mule but there is not enough posts.