Sometimes people like to take random accuracy bits from the original game for no reason better than "it was there" and putting them in their char, without considering the effects that will have when the char is actually being played, and end up making their char behave unproperly or, in several cases, becoming unplayable in certain conditions.
There is a line that should be drawn between when a char can and can't be accurate, and I was feeling like writing about my own opinion on it, it's up to you to give a damn or not. Will list some gameplay elements that should be handled with care and what you should/shouldn't do with them.
Should be kept the same as Kung Fu Man.
I've seen many people changing this just to (namely) go on about "accurate KOF friction!!!", when in fact friction usually varies with each move so the only time the constant should come into play is when the character is getting hit, a situation where compatibility should be definitely favoured.
Why not change it? Many characters count on the opponent to use the standard friction constant (0,85) to determine how far it should slide when attacked on the ground, so lowering this value will make your char end up not far enough and being open to a larger combo than it should, while increasing it makes your char slide away to safety as if ice skating.
So keep these constants at their default level (though I kinda violate this "rule" by making crouching friction the same as if standing) and use "N" physics plus Velmul to reproduce the right friction for a given move.
The other side of the argument on this one says that accurate friction produces better results when facing an opponent from the same game, which completely ignores how large the number of chars out there is, and would make the char work properly if the opponent comes from the same game/series (2% of all chars?) and its author used accurate friction (0,1%?) while being screwed up against all the rest.
Never entirely remove this.
Several gameplay systems rely on this feature to end juggling combos (SFA3, GG, MB), so by removing it you're dooming your char to be juggled forever (usually) if he runs into such an opponent. If you really must disable manual fall recovery, I suggest making it so that the character automatically recovers when allowed to, and, if you really want to kill aerial fights when a char recovers, just make him invulnerable until he lands (just don't make him both invulnerable and with control).
Invulnerability on Safe Fall/Ground Fall Recovery
I only realized this recently, but the char should be invulnerable during the whole animation even though accuracy (to some games) says to make him vulnerable on the last frame(s).
The reason behind it is that chars who can OTG (hit a fallen opponent back into the air) can keep doing it forever if Ground Fall Recovery, usually the only defense against it, does not grant the char a chance to return to an idle state, since they can keep hitting your char out of the recovery and back into the combo.
So, the invulnerability on State 5201 should not be changed, but you can always make alternative kinds of recovery be vulnerable without breaking anything, for instance KOF chars should have invulnerable Safe Fall but vulnerable (at the end) Forward Safe Fall.
Can or cannot be removed. Whether an attack should allow your char to air guard it should be defined by the opponent, not your char, so removing it doesn't really help any of them.
Removing it might however cause some funky situations where the opponent can spam attacks that are supposed to be blockable midair and get an advantage he shouldn't, but this one boils down to how balanced the chars are between each other in other areas.
What shouldn't be done, however, (and I've seen it done, and pointed it out to no effect) is removing air guard from your char but let the opponent air guard your own attacks, perhaps for obvious reasons.
CLSN2 on getting hit animations
Whatever you do, just don't make them as tiny as Kung Fu Man's...
For standing and crouching get hit animations (anims 5000 to 5027), Clsn2 should be exactly the same as in the idle stance and crouch (0 and 11), to ensure your char doesn't miraculously break out of combos. This bit can be confirmed in some Capcom games, but in SNK games (namely KOF) they are basically the same but still vary a bit according to the position of the char's upper body. I personally favour the first style of making them (even for KOF chars) for a reason stated before (when getting hit, compatibility > accuracy) but the latter isn't so bad and can be easily justified. Just never make them too different from their idle counterparts.
Oh, about the opening statement, I was talking about Clsn2 on aerial get hits, Kung Fu Man's are just too small to juggle him properly and nothing like you see in fighting games. So just make sure those Clsn2 are large enough to not let your char fall through a Shoryuken that should've hit (but don't make them huge either).
Dizzy/Guard Crush systems
These are outside of Mugen's common system, so do whatever you prefer if you choose to use either of them.
Wasn't gonna mention this one, but there is something I'd like to say about it and that is dizzy systems should be coded for the opponent, not your own char (if not going to code for both). Why? Because dizzying is part of a game's combo system, if you manage to cause a certain ammount of damage on the opponent, the game rewards you with one more free combo. So coding it for the opponent allows you to reproduce your char's dizzy combos from the original (accuracy up) while coding it for your own char extends the opponent's combos when it shouldn't (accuracy down for the opponent).
Ended up this long because I was planning to move it to the tips section after discussing it.
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