if you have 4 mana after zeph, and the only minion that the opponent has is a taunt + deathrattle minion, you’ll get hex 99% of the time.
With vargoth it probably doesn’t work, but with infiltrator it worked every time for me (with 4 mana; when i had 5 it didn’t)
unless its low stats, at that point you are more likely to get SW pain and board development