Photon Blasts!
So you can use the Y button to donate 10% of your charge to another players Photon Blast during their cast time (before you lose control of your character and the animation plays). It increases the strength of the blast and also counts as a tag for you to get exp from anything it hit/kills. You'll also get any benefits from the support ones (resta or shifta/deband) as well as revive if you were dead.
You can chain PBs with other players if you activate yours in the same time frame. This makes them a lot stronger than if you just donated. This is important for late game content because if you manage to chain into Mylla & Youlla, you'll get a very high leveled Shifta/Deband casted on the party. You cannot chain together the same PB in succession, they must be separated, so no Pilla, Pilla, Farlla, but Pilla, Farlla, Pilla works!
Donations can be done from anywhere, Chains must be in the same room.