The Bundle of Fireworks is a returning item in Risk of Rain 2. They automatically activate whenever the player interacts with anything on the map, which includes Chests, Shrines, and even Barrels. Upon activation, 8 fireworks shoot out from whatever was interacted with, which home in on enemies and deal 300% damage to them in a small blast radius.
In the universe of the game, Fireworks were made illegal on Earth after a series of terrorist attacks, they had disguised their homing missiles as fireworks. They were re-legalized for residential use in 2054.
"Hey, happy anniversary! You really thought I forgot? Ah, I thought I was the dumb one in our relationship. C'mon T, of course not! Well, I wasn't going to let a little alien death planet ruin our night. Right? Shh, just watch. Just watch. It's okay. Just watch. You'll love it - you really will. Then we can go home. You can keep your eyes closed. Just listen. Ah - here it comes! In five... four... three... two... ONE...!"