Useless information:
There was an invisible guard meter in MB. If you blocked enough attacks, your character would get a reddish tint and then get guard crushed and take 300% damage.
Vital Source when depleted made you dizzy, though not the traditional dizzy. No air recovery whatsoever (though it's not like there wasn't more than enough stun anyway), longer hitstun on the ground, and possibly more stuff that I can't remember.
You could deplete Vital Source in several ways. First and foremost, hitting the opponent did this very well. Stuff like backdashing/dashing/airdashing decreased it, I think shielding did too.