Riot's own text for each slot, in the order the champion learns them.
PASSIVE HEADSHOT
Every few basic attacks, or against a target she has trapped or netted, Caitlyn will fire a headshot dealing bonus damage that scales with her critical strike chance. On trapped or netted targets, Caitlyn's Headshot attack range is doubled.
1 PILTOVER PEACEMAKER
Caitlyn revs up her rifle for 1 second to unleash a penetrating shot that deals physical damage (deals less damage to subsequent targets).
2 YORDLE SNAP TRAP
Caitlyn sets a trap to find sneaky yordles. When sprung, the trap reveals and immobilizes the enemy champion for brief period, granting Caitlyn an empowered Headshot.
3 90 CALIBER NET
Caitlyn fires a heavy net to slow her target. The recoil knocks Caitlyn back.
ULTIMATE ACE IN THE HOLE
Caitlyn takes time to line up the perfect shot, dealing massive damage to a single target at a huge range. Enemy champions can intercept the bullet for their ally.