Projectile Clashing
The way Projectile Clashing works in Marvel Vs. Capcom 3 is that anything that counts as a Projectile is assigned a "strength," basically a value of how what it can beat. When two Projectiles clash, the Projectile with the higher strength will win and pass through the other Projectile, but the winning Projectile's strength will have been reduced by the strength of the Projectile it beat and, thus, can start losing to weaker and weaker Projectiles.
Every Projectile in Marvel Vs. Capcom 3 has these values and, during the course of the next few weeks, hopefully we will be able to map out all of these values. So keep your eye on this section and we will update this section as more and more research is done on the Projectile strength values.