Two-Drops
Goblin Cratermaker: This is for two cards in particular: Karn, Scion of Urza, and Treasure Map
. Yes, Treasure Map. Because, again, if it's worth running, it's worth killing. Also, it can pop small dudes, which is nice.
Lava Coil: The other two. Better against control and midrange where I need to deal with strong creatures, but not necessarily the turn they hit the ground.
Sorcerous Spyglass: Lets me scout for wipes, and, more importantly, helps me shut down Vivien Reid, Teferi, Hero of Dominaria, and Karn, Scion of Urza. Potentially, it could also hit Adanto Vanguard and keep it from making itself indestructible, but I've yet to try actually doing that. It's also counter-board against Sentinel Totem and Thrashing Brontodon, though that's even more niche.
Three-Drops
Fiery Cannonade: Explode elves and/or weenies, or at least tries to. Monored doesn't have a lot of good board wipes right now, kind of hoping Ravnica Allegiance will give me more toys. C'mon, Rakdos!
Risk Factor: Better than Frenzy when I'm racing and need to kill a combo player before they can go off.
Four-Drop
Experimental Frenzy: Better than Risk Factor against decks that play the long game, or have good discard access. Basically, anything that knows exactly how it wants to answer the Factor question every time.
X-Drop
Banefire: I tried using Inescapable Blaze here for a while, because I didn't see myself ever casting it for less than six, and liked the instant speed. In the end, though, I realized the real weakness was that I couldn't use it for more than six, severely limiting my ability to close out games that ran long.
Land
Detection Tower: Kind of on the fence about this one. One main, one sided? Just one sided? None at all? It exists for the niche ability to yank hexproof off Carnage Tyrant, Chromium, the Mutable, and Shalai, Voice of Plenty, but also because if I tilt my curve further backwards with spells like Banefire and the fourth Frenzy, I might need that land to help smooth my drops. (And in the other direction, I sometimes side out a Mountain if I'm going super-aggro against combo decks and don't care about Frenzy.)