How are you usually winning games? What I mean to say is, what is the deck style and what are typical plays?
I would try -1 Pillar of Flame +1 Mizzium Mortars
You have the mancer so the mortars is much more playable.
I would also try -1 Wild Guess -1 Blustersquall.
I'd rather have more burn in here or more draw. Tapping their creatures might give you a chance to play a mortars next turn but with a 1 off it won't come up too often. I'm assuming you don't have more mortars though so maybe adding 2 Thoughtflares instead of the wild guess and bluster squall would help.
If you don't like Thoughtflare you could try reforge the soul. It's good for burn decks since they run out of steam rather quickly.
Another thing I've thought about is getting rid of Krenko's command and putting in a Frostburn Weird. It can hold off creatures more effectively and can help wall while you burn the player directly or while you wait to draw out a guttersnipe. It can also draw some bill spells away from the guttersnipe and the mancer. It's a 2 cmc so it'll come out before the snipe to do blocks if need be.
Plus, if you run out of cards and aren't drawing anything, you can try swinging in with the weird. It's really flexible.
So maybe in the end you could do
-1 Pillar of Flame
-1 Wild Guess
-2 Krenko's command
+ 4 Frostburn Weird
+ 1 Mizzium Mortars