Too lazy to post the whole thing here, but the patch notes are here.

Important stuff in 3.12:
Jiiiiiinx
Olaf rework
Garen VU
Phage/Triforce nerfs
Trade system no longer sucks
Probably has Creator Viktor and Championship Thresh

Champion rotation: Heimerdinger (twice in one year holy ****), Morgana, Sivir, Soraka, Kennen, Shyvana, Volibear (woo), Zyra, Syndra, Quinn