RYNO is the secret weapon in Ratchet & Clank Rift Apart. This guide explains how to get the RYNO. This also unlocks the trophy Aim to Misbehave.
Simply put: You need to find all 10 Spybots. Each Spybot gives you a blueprint for the RYNO. Afterward, you can buy the RYNO from Ms. Zurkon, the weapon vendor.
Spybots are the Collectibles that look like little orange robots. In the planet select of your spaceship (unlocked after 2nd planet) you can see how many there are per planet and how many you’re missing. They get marked on the map when you are close to them.
The RYNO is the best weapon in the game. It causes a lot of damage over a wide area and instant-kills most enemy types. Each shot will create a dimensional rift in the sky that rains down heavy objects onto the enemies and causes a purple explosion. The only drawback is that in order to get the last Spybot you have to reach the end of the story first. So it takes a lot of progress and is only really useful for Challenge Mode (New Game+). Below are pictures of the weapon and what its shots look like.