I'm really curious about the single player unlock conditions. Everyone seems to have gotten certain characters in different ways. Though I don't think people have looked outside of Classic mode much yet.
The easiest known method is # of Versus Matches. Every 10 matches results in a new challenger, up for 120 total matches for the last one. You don't need to win those matches, and every failed attempt at unlocking a new character immediately lets you retry after the next match. The fastest method that I know is 1 stock, play as Sonic and versus CPU Bowser (short victory animation), run offscreen and suicide. Repeat until all 12 are unlocked.
My verdict on Mega Man: best move is Slash Claw. All of his other moves in particular are mediocre. In general, they suffer from:
- complete lack of guaranteed combos
- lack of priority (can cancel most projectiles but can't pierce)
- lack of damage
- lack of knockback i.e. killing potential
- lack of range
- susceptible to so many hard counters (pocket, Link's shield, reflectors, etc.)
- too much endlag -> too linear (e.g. Samus's missiles have a slow startup = can attack during missile = multiple vectors of attack)
Mega Man seems to thrive on positioning (i.e. trying to manipulate your opponents to move in unfavorable ways, usually through projectiles) and straight up gimping. In particular, throwing and Top Spin can push opponents outwards from center stage, Sliding can protect the ledge. Offstage Slash Claw is the best way to kill enemies, especially since it's very useful against characters with relatively poor recovery (e.g. Link), even at low %s. Otherwise, Charge Buster to capitalize on certain situations like reading rolls.
Metal Blade: not very useful except maybe protecting recovery.
Crash Bomber: can force opponents to shield or jump, usually misses or gets canceled, but if it manages to hit, it can kinda be followed up by charge buster
Leaf Shield: useful for grabbing, otherwise way too much startup, pathetic damage, don't throw it.
Rush Coil: apparently a glitch/exploit can negate certain knockbacks that are nontumble. Haven't really tried it myself. Otherwise, self explanatory recovery (can midair jump after using it).