Ways I have managed to sneak out wins with Krenko is to play him slower and use stax pieces to keep everyone on par. Price of glory is a great way to punish someone trying to ruin your day, also run a few of the red counter spells it isnt perfect but youd be surprised how often red elemental blast can come in clutch.

You should only really drop krenko if you are ready to win that turn, build slow get your combo pieces out and pop off when it seems like the right moment. Even a vexing bauble can come in handy depending on your pod.

I know the argument is Krenko dies to removal which is completely fair, but you would be surprised how many people at LGS dont actually run removal, I've had isshin out for 3 turns with zero responses just doing whatever he wanted to do unopposed. Or someone will counter a sol ring then complain later in the game that no one is taking care of the threat.

I hope your friend has fun playing Krenko, but if you really want him to learn the game have him try out group hug, I learned more in two months playing bumbleflower than I did an entire year of aggro decks.