Originally Posted by XSV Brutal1ty
Katarina is one of the more difficult players to play
Both champs are incredibly powerful, but are also easilly countered, thus, timing is important, and knowing when to enter a team fight.
For Kat, wait until someone initiates and a little after than, then jump in with your combo. Preferably at a squishy, so your cooldowns can refresh quicker. She's very much like Yi in that she needs to be able to kill stuff to be effective. She does a crapton of damage, but again, like Yi, it's over a long amount of time, andwithin that time she's very vulnerable.
For Yi, you'll have to wait a little while into a team fight, when enemies have all used their hard CC moves. A Yi's only form of surivivability is basically just killing stuff before it can kill him, and one snare spells death for him and his 1900 meager health points.
Kat and Yi both have rather low skill caps, but the trick is all about timing.