Ori, Nunu, Brand, Zyra, Pantheon. As long as they all get clustered in the middle and get hit by Pantheon on his descent, looking at over 2000-3000+ damage on every champ depending on resistances (this is level 18 with full builds).
Different response than most of the ones here, but this was a nasty one as well. Ran into a "protect the kog" pre-made team a few days ago. AP Janna, support nunu, shen top, and jungle sejuani.
-Janna slows, knockups, and knockbacks. Shields kog if necessary. -Shen builds pure bruiser. Anybody gets close to kog he taunts them and/or ults kog. -Nunu ult as a spacing tool/slow. Snowballs keep you away from kog. Bloodboils the kog. -Sejuana slows the hell out of everybody and has an amazing ult for keeping people away.