Cleave, Multi-Shot, Swipe, Chain Lightning, and Avenger's Shield will no longer hit targets that are under the effect of CC spells that break on damage, such as Polymorph or Sap. This includes Felguard Cleave and the Chain Lightning effects caused by various items. As far as I can make out, this is all spells that hit multiple targets, but are not AoE; Thunder Clap, for instance, will still break sheep. Edit: Whirlwind, Sweeping Strikes, and Blade Flurry do not seem to be included. Overall this change is, frankly, awesome. The implications for tanking alone are highly pleasant, as well as for Hunter and Elemental Shaman DPS. I'm starting to get excited about patch 2.4 all over again.