OHK doesn't work on Defend The Goodies!
I don't know what is wrong or why it doesn't work, but when I use OHK in Defend The Goodies! it brings the present's health down to almost zero, but the minions that spawn seem to have the same amount of health they normally would. And, as a result, I can't easily solo Defend The Goodies! =(
Theyre immune. Make yourself small and spam snowballs instead.