Slim Cognito is looking to build a RYNO superweapon. Find all RYNO holocards and he'll make you one.
Collect all RYNO holocards and Bring all RYNO holocards to dealer are missions in Ratchet & Clank (2016 game) taking place in Blackwater City, Rilgar. After Ratchet and Clank found the Shady Salesman following "Escape the sewers!", he granted them a Trespasser to help look for holocards with plans for the RYNO. The two obtained all holocards and he constructed the RYNO for them.
Nine RYNO holocards are obtained, with the final holocard obtained on the second visit to the Deplanetizer. At this point, travel to Blackwater City and speak to the Shady Salesman to be given the RYNO, the most powerful weapon in the game. This will easily prepare you for the final boss.