Embermaw Hellion is a legit bomb who boosts all of your red spells. 5/5 for 5 is powerful in this meta. I would cut some of the renown stuff, flameshadow conjuring and infectious bloodlost to fit in all the early burn - twin bolt and fiery outburst.
I may be wrong about flameshadow conjuring - it just feels win more in this deck. If you can afford to spend a turn ramping and then spend a turn casting this spell you probably should have won already.
I was looking at
Embermaw Hellion when first building the deck but ended up cutting him due to a lack of Red sources in the deck. Of course later on more red found it's way in so it might be worth reconsidering his inclusion. Likewise with the
Infectious Bloodlust - something I'd want to try out but would be willing to cut should they under perform. Most likely for either
Fiery Impulse or
Twin Bolt as you had suggested.
Flameshadow Conjuring is something I will be sticking with for a least the time being. It's a fault of my playstyle - I tend to be overly conservative when playing (something that always hurt my aggro decks) and Conjuring gives me a perfect excuse to just go wild a throw things without a care. True it's a little win-more but I still think it's a addition that can carry it's weight.