Pentarina's I MEAN Katarina's combo is very easy to use. But it needs to be used at the exact moment.
COMBO:
Q + E + W + R

Katarina's Pro's:
+In good hands, she makes masacres
+Very Strong at late game and Team Fights
+Good amount of damage
+Lot's of Champs are weak for her
Katarina's Con's:
-Weak at early game :C
-Weak at enemys with magical resistance
-In bad hands she makes disasters
-Easy to KS a ally

´´Driven by an intense killer instinct, Katarina uses her talents as an assassin for the glory of Noxus, and the continued elevation of her family. While her fervor drives her to ever-greater feats, it can sometimes lead her astray.
From childhood, Katarina displayed a natural gift for combat. As the daughter of a prominent Noxian general many paths were open to her, but she rejected them all for the path of the blade. Rigorously trained by the finest assassins in Noxus, her father the best among them, it was not long before Katarina demanded her first assignment. The task they gave her was aggravatingly simple: assassinate a low-ranking Demacian officer. As she set to her work infiltrating the enemy camp, Katarina discovered an opportunity too tantalizing to pass by - the arrival of a Demacian General. Stalking him to his tent, she quietly dispatched his guards and slit his throat. Pleased with her impressive kill, she disappeared into the night. Katarina's elation faded the next day when her original objective, the Demacian officer, led his forces to ambush unprepared Noxian soldiers. Though the Noxians fought valiantly, they suffered heavy casualties. Furious at her mistake, Katarina set off to complete her original task. Returning to the camp, she spied her now heavily guarded target and realized a stealthy kill was no longer possible. Drawing her blades, Katarina swore the officer would die, no matter the cost. She leapt into battle, unleashing a whirlwind of steel. One by one blades flashed and guards fell, each strike bringing her one step closer to the officer. A final thrown dagger restored her honor. Bloody and bruised, Katarina barely escaped the Demacian forces, and returned to Noxus a changed woman. The scar she earned that night now serves as a constant reminder that she must never let passion interfere with duty.´´
"Never question my loyalty. You will never know what I endure for it."
- Katarina

-Provoque your enemy, using Q + W
-Use Ignite + Flash
-Your E can be used in WARDS
-Put a ward and use E to chase an enemy