You might be wondering about Young Pyromancer, and it's certainly fine filler in mono-red, but these decks usually have no more than five instants or sorceries, so Young Peezy is not a premium card like it is in blue-red builds
Just ask
The cut is almost surely some of the previously mentioned Sam Black resource conversion stuff, and the empty sideboard slots are likely best as Collective Brutality
If the player doesn't, you mill three cards, then this creature deals damage to that player equal to the total mana value of those cards
Loxi: Another card that you probably should run in your big E decks, but I think it's super helpful towards the archetypes they're pushing besides "ramp and play your gigantic dude," so I'm all for it
Oh, and of course, theres the dash ability to talk about