And the card is.....
Board wipes are obviously good at punishing aggressive decks like Ramunap Red but there is a very specific reason that Fiery Cannonade is actually better than the alternative I have seen in a few red sideboards which is Sweltering Suns.
First of all, Fiery Cannonade costs two colorless and a red rather than one colorless and two red, so it is slightly easier to cast when you might have a field full of Sunscorched Deserts and/or Ramunap Ruins and don't want to unnecessarily ping yourself. Unlikely but hey it might happen and every little advantage counts.
The second, and most obvious, reason it is better is that Fiery Cannonade is an Instant while Sweltering Suns is a Sorcery. This allows us to pass the turn, see what the other Ramunap player drops, and then Cannonade after attackers are declared to potentially hit one extra haste creature and get added value. Additionally, assuming it clears their board and they can play nothing else (perhaps from tapping out from playing an Ahn Crop Crasher or something), then on our turn we will be able to reset the tempo by playing the first creature onto the battlefield. This is really strong, especially when you're on the draw and at a huge disadvantage to begin with. Resetting the tempo can negate their choice to go first and as any Ramunap player knows, going first is huge for this deck.
The third reason Cannonade is better than Sweltering is because Cannonade does two damage instead of three. Now you might be thinking to yourself what kind of noob is this guy, he thinks two damage is better! It hits fewer things!
- Turn 1: Soul Scar Mage
- Turn 2: Kari Zev Skyship Raider
- Turn 3: Pass to them. On their turn, play Fiery Cannonade. Prowess triggers on your Soul Scar to buff it to a 2/3, thus he survives. Kari Zev at three toughness survives.
For the sake of this article lets assume your opponent went Turn 1 Bomat Courier, Turn 2 Earthshaker Khenra, and Turn 3 Ahn Crop Crasher. Now this would normally be a very fast and good opening three turns for Ramunap. Suddenly all three of his creatures die and the two dudes you played both survive.
Obviously this is a best case scenario situation, as maybe he played a Turn 2 Kari Zev which would survive this (but that is also why you wait until attackers are declared so at least you can kill the monkey and avoid the two damage there).
The point is that even though Sweltering Suns would assuredly kill more of your opponents threats, it also kills everything you have played too. It won't actually help you regain any tempo unless you intentionally don't play creatures before using it. Even then, you have to play it on your turn so your opponent gets to play the first creature back onto the battlefield again. Fiery Cannonade might not have those drawbacks. It might kill your opponents threats, while allowing your stuff to survive. That's why it's better. If the scenario I outlined above happened, it would be very, very difficult for your opponent to recover and regain the tempo needed to win the mirror match.
As an added bonus it also is very good against Mono White Vampires!