I need to be clear up front that I'm not presenting this as a strong choice for the current Standard metagame. I'm sharing it because I think it's cool and maybe has some potential, but I'm struggling to win with it. Suggestions are welcome.

I stumbled across the combo between Calamity, Galloping Inferno and Terror of the Peaks while brewing something for the OTJ Constructed Midweek Magic event. Then a couple of days later I saw that PowrDragn had posted a video on a similar theme (he's actually done Gruul ramp several times in the past few weeks, but that video is the closest to what I'm posting here).

So I've kept working on a Standard-legal version. The goal is to field Calamity along with another creature that will put the game away if it saddles Calamity. Ideally you'll win on the spot, but setting up to win soon afterwards is an acceptable consolation prize.

I've been playing this in best-of-three ranked matches on Arena and, like I said, it's not putting up the results I would like; opponents have plenty of relevant disruption. Trying to surprise people with it in best-of-one games might be a better plan. But, eh, it's fun when it works, and I still feel like there might be a good deck under here if I can work out the right configuration.

The list

About
Name Asteroid Horse

Deck
5 Mountain
4 Forest
2 Boseiju, Who Endures
1 Sokenzan, Crucible of Defiance
2 Commercial District
4 Karplusan Forest
4 Rockfall Vale
2 Conduit Pylons
1 Bucolic Ranch
3 Tamiyo's Safekeeping
3 Scorching Shot
4 Smuggler's Surprise
4 Armored Scrapgorger
4 Bramble Familiar
1 Ruby, Daring Tracker
3 Outcaster Trailblazer
1 Topiary Stomper
4 Railway Brawler
4 Terror of the Peaks
4 Calamity, Galloping Inferno

Sideboard
3 Pick Your Poison
1 Pithing Needle
1 Unlicensed Hearse
3 Brotherhood's End
4 Obstinate Baloth
2 Tyrranax Rex
1 Titan of Industry

Card choices

Ramp creatures

There are other possibilities, but these are all the mana-producing creatures I thought were worth an audition:

I considered non-creature ramp spells, but the ones available in Standard right now don't excite me. Reprint Rampant Growth!

Saddlin' up

This list includes some creatures that aren't in my current build, but that I think combo well with Calamity (and perhaps each other) and are definitely worth consideration.

N.B.: While Calamity creates two tokens as part of the same ability, the tokens enter one after the other. The original creature sees the first token enter. Then the original and the first token both see the second token enter.

I experimented with various configurations, but I've gravitated towards playsets of Railway Brawler and Terror of the Peaks. They work well with each other, and are the most likely of the options to be able to win the game on the spot when they saddle Calamity.

Other spells

The Calamity combo is pretty disruptable: opponents can remove Calamity, of course, but they can also remove the creature saddling it in response to the token-producing trigger. I put in Tamiyo's Safekeeping to try to defend against that. There are several similar spells in Standard, but I like Safekeeping for a couple of reasons: it protects from some board wipe spells, and the lifegain might be relevant against aggro.

I never like to be completely without creature removal, and I think Scorching Shot is the most efficient removal in our colors at the moment. However, I often end up sideboarding it out in match-ups where it's not relevant. I could be convinced to replace it with something else. I previously experimented with Strangle, and might go back to that.

Smuggler's Surprise on the opponent's end step is one of the ways we try to work around control decks. If they don't counter it, great, and if they do, you can untap and try to cast the creatures themselves. Ideally you'll cast it for eight mana, but if the best you can do is flash in one creature for six mana, it may still be worth it. In a pinch, you may find yourself casting it for three to dig for lands.

Before I saw PowrDragn's video, I was running Commune with Nature in the Smuggler's Surprise slot. Commune made the deck more consistent -- it's cheaper and looks at more cards -- but Surprise makes it more resilient.

Lands

I'm running zero Copperline Gorge and only two Commercial District because I think it's essential to have untapped mana on turn 5 or 6 when you're trying to land your big creatures. This deck does nothing on turn 1, so Rockfall Vale is only bad on turn 2, which is easy to work around as long as not all the lands in your opening hand are Vales.

I think we may start seeing Conduit Pylons popping up in unexpected places. Getting a free surveil on a land that enters untapped is pretty good. I rarely have color problems in this two-color deck, so a couple of Pylons aren't too much to handle.

Calamity is the only card in this deck that Bucolic Ranch can put into your hand, but even if that doesn't happen, repeatable scrying can still help you break late-game stalemates.

I tried Cavern of Souls in an early build, but it's tough to know what to name because no two creatures in this deck share a type.

Sideboarding

I used to see people putting Obstinate Baloth in their sideboards and think, that's a huge swing if you can make it work, but how often will it actually happen? Well, this deck, and this metagame, are the Baloth's time to shine. Bring it in against Boros Convoke and other aggro decks, where a little lifegain and a big blocker coming down as early as turn 3 can really give them pause -- and if you live long enough to see it saddle Calamity, it'll probably put the game out of reach. But also bring Baloths in against Grixis Crimes or any other deck with multiple open-ended discard effects like Hopeless Nightmare, Tinybones Joins Up, Liliana of the Veil, or Aclazotz.

Pick Your Poison is a good substitute for your removal spells in the Atraxa Domain match-up, equally worth casting against Up the Beanstalk, Spelunking, or Temporary Lockdown early, and Atraxa or Archangel of Wrath late. I'd also bring it in against Slogurk/Rutstein legends and try to snipe their Relic of Legends as soon as possible.

Brotherhood's End is of course good against aggro, and should also help you fight back against Simulacrum Synthesizer strategies -- not all of their artifacts cost three or less, but enough of them do. None of your mana-producers survive Brotherhood's End, but as long as it gets more of the opponent's creatures than your own, that may be a fair price to pay.

Tyrranax Rex is primarily here to force its way through counterspells, although now that control has an instant-speed wrath in Final Showdown, it may not be the panacea you'd hope. The toxic dinosaur can also be worth bringing in against decks that gain a lot of life, such as Orzhov Amalia/Voice of the Blessed strategies, and Atraxa Domain.

Unlicensed Hearse comes in to support your Armored Scrapgorgers in the match-ups you'd expect: Slogurk/Rutstein legends, Azorius Djinn & Mentor, and anything playing Aftermath Analysts.

I like having one Pithing Needle for general interference purposes. It's cheap hate for Restless lands, planeswalkers, and combo pieces such as Aftermath Analyst, Rona, Herald of Invasion, Slogurk, the Overslime, etc. If you know your opponent's deck, you can feel fairly confident naming one of those things blind on turn 1, when you weren't doing anything else anyway.

Known bugs

There is a reported issue on Arena where Calamity will only produce one token, not two, if the opponent controls a planeswalker. (Please go vote for it!) It happens consistently and it's a pretty serious drawback.

What does "Asteroid Horse" mean?

A couple of days after I started working on this deck, I was watching a livestream concert (not Magic-related) and the streamer responded to a question from a chatter named "Asteroid Horse". I thought it was a cool name and a fitting one for this deck. I don't know the chatter nor where they got the name from. There was apparently an undefeated thoroughbred racehorse named Asteroid, so maybe that's it?

What is going on here flavor-wise? Is that a dragon riding a horse?

I don't know what to tell you. Saddle doesn't make any sense to me either.