Princess Cannon

The Princess Cannon is a special weapon in Splatoon 2. It is not part of any main weapon's set, and is instead only available in the final Shifty Station layout, MC.Princess Diaries, where it appears in the middle of the stage when there is one minute left until the battle ends. It is similar in appearance and function to the Killer Wail from Splatoon, although the beam is much larger and it takes a little longer to charge up.

Octo Expansion
The Princess Cannon is used in the Turf War final battle against Commander Tartar in the Octo Expansion.

After asking for help or covering the NILS in ink, the statue still fires its sanitized ink laser out of its mouth at Inkopolis. Pearl uses the Princess Cannon to counter the sanitized ink beam. As she fires the Princess Cannon, the score screen shows up, showing the percentages very similar to the turf war percentages. Pearl wins by 888.8%, and the meter cracks, similarly to how it does in Ranked Battles.

In MC.Princess Diaries
For the last day of Chaos vs. Order, MC.Princess Diaries was an exclusive stage for the Splatfest. When the clock hit one minute left, Pearl arrived in the center of the stage and waited for a player to get close to her. When a player got close to Pearl, she gave them her Princess Cannon and allowed them to aim it. Pearl helps the player to fire it and leaves.

It is still able to be played on MC.Princess Diaries in Private Battle and the Princess Cannon is available to use.