It is still a bit lean on mana, but it can still "limp" on 2 or so mana and still win with combos with only 2 mana. If it gets to 3 mana there is only 1 spell the deck can't play, but it's a good one at Torbran, Thane of Red Fell. So I might still dial back the burn spells for another land or two.
Removed...
1x Shock for 3x total instead of 4x. I have too many burn spells after recent changes, and replacement somewhat covers the role too.
3x Chandra's Outrage with trying to keep the cmc low, it was just too inflexible and expensive for the mana curve of the deck. I could use Slaying Fire for 1 less mana to burn a target, and while I lose the potential combo for Chandra's Spitfire or the spectacle cost on Light Up the Stage I'm unlikely to have enough mana to combo until late game where creature toughness is too high for the burn itself.
3x Burning Prophet the scry and extra damage from spells is nice, and having 3 toughness meant I could block 1st turn easily or live through some burn like Shock. It was not nearly as "Impactful" on the deck as some replacements though.
3x Mountain removed for utility lands
Replaced With...
3x Chandra's Pyrohelix So straight compared to shock it can be a downgrade, but if we look at the deck itself the flexibility provided can help a lot more. For example say the enemy has two creatures with 1 toughness, shock could only get 1 where this can get both. I can also use the split to kill a low toughness creature and the other damage direct to player to trigger spectacle costs on Light Up the Stage or trigger the ability on Chandra's Spitfire. Lastly if Torbran, Thane of Red Fell is on the field, this can turn the spell into 6 damage! (3 on one target, 3 on another.) Worst case scenario it's a less efficient Shock, but that's why I kept both in the deck to spread out versatility in the burn spells.
3x Chandra, Acolyte of Flame one of the +0 will easily trigger Cavalcade of Calamity and can combo for wins itself with enough time or with Chandra's Spitfire to buff a lot in a single turn. With Torbran, Thane of Red Fell it can turn them into 3/1s as well. The -2 ability can let me replay pretty much any spell as well if I have the mana to cast, as all my instant/sorceries are 3 cmc or less
4x Castle Embereth Being mono red means I'll always have mountains for it to come into play untapped. With the changes I net gained 1 land for a total of 21 which is still kinda lean and does lend to some mana droughts.