I'm writing this just before the release of Khans of Tarkir Limited on MTG Arena. Khans is a beloved Limited format that is well-balanced and has a lot of replayability. Most importantly, it's the format of the December 16th Arena Open.
Khans of Tarkir holds a special place in my heart, as it was my first Pro Tour top eight, and I ran off a 5-1 record in the Limited portion. Khans is an excellent competitive format, and it's also a good time. I'll run down some of the set basics and discuss strategies that worked well for me.
Morphs won't trick you!
Let's get to the basics first. Morph is a key mechanic, so the creature sizing might be smaller than you're seeing these days, which also leads to slower games. In the original morph sets, there were often ways to get your opponent with morphs. The classic is a Battering Craghorn or Skirk Commando conundrum that existed during Onslaught, the original morph set, and doesn't exist in Khans. Creatures only size up for five mana or more, so on turn three you can never lose a combat blocking their morph with your morph, and you should usually take the trade if you're on the draw because they're going to get to five mana first.
Since they're incentivized to block, you should play your worse morph more often on turn three to attack their morph if you're not going to be playing an actual four-drop.
Keep in mind you're always safe to block until they have five mana. They can have a combat trick, but that situation would happen sooner rather than later.
Stay as close to two colors as possible
While the set is designed around three-color cards and such, you still want to have two main colors and splash a third or even fourth. It's important to make sure your main two colors are consistent and pick up lands when you can to enable splashes. A lot of the format's most powerful cards are gold, so you want to slide them into your deck, but you don't want to cast three different colors of cards regularly. While morph allows you to make plays even if you're missing a mana color, it's still important you don't fall too far behind, especially in a Bo1 setting where a lot of this format will be played.
Ideally, your mana base has at least eight sources of your two main colors and about four sources of any light splashes of up to three or so cards. If you have more than that, try to get more lands and fixing to allow you to more consistently cast your off-color spells.
You can still be aggressive!
Aggro decks are still viable and some of the format's best decks. While I often tried to have a slower, more controlling approach in the format, the meta-strategy created during the Khans Pro Tour by the Cabin Crew, now known as the Czech House, forced a Simic Aggro deck that was streamlined to two colors as much as possible and occasionally had light splashes.
Two-drops like Smoke Teller, Highland Game, and Wetland Sambar that curve into heavy hitters such as Alpine Grizzly appear weak on the surface. However, when backed up with tempo-pushing spells like Force Away, Crippling Chill, and Savage Punch, they can punish slower or less consistent four- and five-color decks effectively.
With BO1 hand smoothing in the mix, I can only imagine this archetype is strong.
I remember thinking the strongest archetype going into the Pro Tour was Mardu-based token decks. Trumpet Blast and Rush of Battle were excellent ways to close a game. Mardu Hordechief and Ponyback Brigade are the premier commons for this archetype and two of the format's best commons. These cards made it easy to push through for enough damage while opponents were stuck on one play per turn, which was common given the format's focus on morph. Mardu Hordechief was the format's best common and a good signal that white is open if you're seeing them pick three or later.
Play an extra land!
There's not too much to add to this, but getting to five mana with morphs was pivotal. Whatever number of lands you're used to playing, add at least one. It will help you cast spells by adding a colored source and help make sure you hit that key five lands. There's a decent amount of card draw with cards like Treasure Cruise and Bitter Revelation at common, so flooding out isn't that worrisome. You can often spend your mana as long as you have it, so make sure you do!
Five-color decks work, but only if lands aren't contested
Five-color decks were my bread and butter, and I like more slow and controlling decks. When people are focused on smooth curves and sticking to two colors, you can often get lands later and get good-enough mana to play a bunch of colors. You still want to stick to a main color or two, but don't be afraid to branch out if the lands are coming. Playing five colors means you need more total picks for your deck to come together. You have to be getting lands later at some point in the draft or your mana and card quality will likely be too low.
I like my five-color decks to be Sultai- or Abzan-focused and splash in other colors. Black and green have cheap effective blocks to slow the game down with cards like Disowned Ancestor and Archer's Parapet. I only drafted this style of deck when card quality was high. I never went into a draft anticipating getting a high-enough quality of cards to end up here, but it does happen at a high-enough frequency that you want this in your range.
Trail of Mystery was a bomb in the format, and that's a good starting place for five colors if you happen to pick it up.
Diminishing returns on delve
Delve is a mechanic that, as we know from Constructed, has diminishing returns. The more delve spells you have, the worse they are collectively. Your first Treasure Cruise is more valuable than your second. Keep this in mind when evaluating cards. There are premium delve spells, such as Dead Drop and Murderous Cut, but make sure you don't overdo it on delve when you take these early. A card like Shambling Attendants is excellent if you don't get any delve spells. It's much worse when you have more.
This will wrap up some of the quick tips for Khans. The set is a lot of fun and will be slower than you're used to if you started playing after this set's release. I'd get some good practice in before the Open and start studying the morphs and combat tricks because there are a lot of situations where you can use reasonable format knowledge to sniff out exactly what your opponent is trying to accomplish. Good luck and have fun!