When tagging a creation, always use underline characters when adding tags containing multiple words. Dragon_Ball_Z is correct, Dragon Ball Z is not. Separate words counts as separate tags, so using three words in the above example would provide a search result when searching for “Dragon” or when searching for “Ball” both of them incorrect.
Use SPACES to separate tags, do not use commas!

The most important tags are :

tagme – If you don’t know the creation well enough to add the proper tags, use the “tagme” tag to signal to the other users that the list of tags is empty/incomplete. If you find a character with this tag and properly tag it, remove the “tagme” tag after you are done.
Character – The creation is a character
Stage – The creation is a stage
Fullgame – The creation is a fullgame
Lifebar – The creation is a lifebar
Screenpack – The creation is a screenpack
Tool – The creation is a special tool for editing/creating mugen content
Edited – The creation is an edited version of an existing creation of another author
Orig_Author_xxxxx – xxxxx is the original author of the edited creation.

Hi_Res – The creation’s native resolution is 640*480
Low_Res – The creation’s native resolution is 320*240
HD_Res – The creation’s native resolution is 1280*960
Widescreen – The creation’s native resolution has a 16:9 ratio (1280*720)

AI_None – The character has no AI.
AI_Old - The character has winmugenhi beta compatible AI. It ignores difficulty level, and uses workaround code to detect CPU control.
AI_New – The character uses the AILevel trigger of mugen 1.0 to activate AI. It fights according to the difficulty level selected in mugen’s menu.
AI_Only – The character cannot be played by a human player, it is only available as an opponent.

Boss – The character was a boss opponent in the original game. If the character doesn’t have an original game and is new to mugen, this depends on what role the author decides for it. Generally Boss characters of the same game system are harder to defeat, and easier to win by using than non-Bosses, but there can be exceptions.
Hentai – The creation has adult (18+) content of some kind.
Projectiles – The character uses projectiles, beams or other ranged attacks as its primary fighting method
Physical_Combat – The character uses physical combat (fists, throws, kicks, swords, etc) as its primary fighting method
Magic – The character uses magical spells as the primary fighting method. These magic spells might be projectiles, close range attacks, or anything. Any kind of supernatural/spiritual power that doesn’t rely on the physical body falls into this category, like exorcism powers, or abilities of a ghost or monster.
Strikers – The character can call other character(s) for help in battle. Generally the helper(s) perform a single attack and leave, but there are permanent types ones as well. This plays a vital part of the gameplay. Characters that contain multiple fighting units also belong to this group, like the Magic Knights or Youki-so-Suika.

Fighting_Game – The character originates from a commercial fighting game.
Doujin_Game – The character originates from a fan made game of some kind.

Male – The character is a male human or humanoid.
Female – The character is a female human or humanoid.
Animal – The character is a real or fictional animal or monster of some kind (pokemon, dragons, and the like)

Anime and Game titles – If the character comes from an anime or game series, add the title as a tag, like this : Sailor_Moon, Dragon_Ball, Mortal_Kombat, Touhou etc..
Game system – If the character is accurate (or at least has most important elements of) the original game, and the title of that part of the game series, like : Immaterial_And_Missing_Power, Scarlet_Weather_Rhapsody, etc… If the game is known by an abbreviation, add that as well (like IAMP and SWR in the examples)

Chibi – The character is considerably shorter than “normal” mugen characters, either intentionally redrawn that way or because the original game had that size. Characters from old SNES Final Fantasy games would fall into this category for example. They are like less than 30 pixels tall.
God_Character – A character that is obviously designed to be very overpowered for easy victories. They usually have an unnaturally high attack, defense, maximum life, power generation, lots of invincibility frames, and life regeneration. So of them are outright undefeatable, the rest are “only” near impossible to defeat.
Abandoned_Project – The creation is incomplete, and wasn’t updated in a year or longer or the author himself declared he won’t finish it.
Original – The character is not from existing games, but is newly made (drawn) for mugen.
Recognizes_charname_By_author – The character has some custom coded (an intro, fighting mode or anything) interaction with the character named in the tag.
Spriteswap – The character has the same functionality/attacks/gameplay as another character, but the sprites are changed. Example : TES-Koma (Komachi from SWR with Testaments attacks, and voice from GGX)
Eyecancer – Characters that use a large amounts of flashing and vibration effects that is bad for your eyes.

Game mechanics :

Superarmor – The character doesn’t go to the standard hit states when taking a hit, and his attacks are not interrupted. Only add the tag if this applies for the whole character, not if it’s only for specific, uninterruptable moves.
Grazing – The character can run through certain types (or all types) or projectiles without getting hit. It often also removes the affected projectile(s). A mechanic mostly used in Touhou characters.
Guard_Break – The character can only guard a limited amount of hits. If it is hit again, guarding stops, and the character gets hit/stunned. Another mechanic from Touhou games.

If a creation’s name is different from the original, add the original name as a tag. For example, for the Metal_Patchouli character made by Otto, the Patchouli_Knowledge tag needs to be added.