All below directionall inputs will be as such: up = u, down = d, forward = f, backward = b
Wavedashing is something that’s in MvC2 more as result of a glitch. Essentially what you’re doing is cancelling a dash with a crouch, and then immediately cancelling that crouch with another dash. It allows for superfast dashing across the entire arena as needed, essentially. The input in MvC2 for it is basically: PP, d~PP, d~PP, etc. a ~ sign implies pressing the first action (d), almost immediately followed by the second (PP). PP = 2 punches, the button command for a dash.
Tridashing I’m assuming he means trijumping which is a short form of triangle jumping, a concept which applies to any character with an 8-way dash. What you do is jump, then immediately airdash down-forward and press an attack button. This grants your character an instant overhead attack that must be blocked high on reaction in a very small window, making it a great pressure tool to start your offense. A basic input for a trijump would be with Magneto for example: u, df+pp~lk.