Simul mode is currently way too broken gameplay wise and is impossible to code without glitching for the current version of mugen, so I'm doing away with it and replacing it with a tag mode.  I had already decided on it a year ago, but there's a lot of code to consider, so I haven't actioned it yet.  LA has implemented a tag mode in his own stuff in the meantime. So he'll try to help.  Here's where I'm at after the first round of feedback:

Tag in and out freely, but no attack and no invulnerability. A quick pause before an attack can begin.

1 DM stock to do tag out attack.  Simple dive in attack.  The bonus is that there will be full invincibility and strike for 100 points of damage and minimal recovery time.

2 DM stock to do a counter tag in while blocking an attack.  The tagging character will do a special attack for about 300 points of damage.

3 DM stock to do a double team.  Initiates a tag, but both character attack with a DM for upto 500 damage.

2 DM stock to tag out while guarding. Or did you mean something else?