With his Specialist and Growth abilities, Confucius is the ideal leader for the Khmer. From turn one you can put a Specialist in your Capital for +4 Science at the cost of slowing down your first settler. Early Angkor Wat, cards to buff specialists and add growth - it’s all made for Confucius. Even Specialists on Warehouse buildings start to look attractive with the Science from Arogayasala and Confucius combined. Your main obstacle won’t even be the specialist limit or the population - it’ll be the happiness cost. Secure happiness resources like Dyes or Llamas, focus on buildings like Villas, and consider a happiness pantheon.

If dealing with the happiness crisis as Confucius sounds scary, consider Pachacuti instead. Though more restricted by his Mountain affinity, you’d be surprised at the amount of terrain you get bonuses towards with this pair. Mountain Cities fed by Tonle Sap Fishing Towns can result in crazy amounts of food. Pair with Lokesvara and Mandala, and you’ll have no trouble reaching max Pop. Consider also Pithi Chrat giving Food Buildings a river adjacency - your Food Buildings already have an extra mountain Food adjacency as Pachacuti, so it's easy to find high value Garden and Granary spots. Although you don’t need Chakravarti as critically as other civs since the Happiness adjacency next to mountains is free anyway, you can use it to chain celebrations more effectively to benefit from Mandala.

Ashoka has fantastic synergy with every aspect of Khmer’s kit, and is a great pick if you want to be flexible in how you take the game. Specialist focus or going wide (Khmer has no extra settlement caps in their civic tree), happiness or food, he’s your guy. Of particular note is the Baray - the +2 Happiness for adjacent Quarters basically doubles its effectiveness, since Ashoka will have buildings next to the Baray gaining a Happiness anyway since it’s a rural improvement. Use this overflowing happiness to support specialists, or to safely ignore the settlement cap and get insane science from Arogayasala.

Dr Rizal’s ability to chain together infinite celebrations with extra happiness towards celebrations and extra celebration length means he can get constant uptime on Chakravarti and Mandala. Chakravarti may as well be a ‘your specialists have no happiness maintenance’ card on Jose. This can effectively guarantee you complete the Science legacy path in Exploration, leaving you open to focus on Treasure Fleets or generating Relics.

Trade Xerxes has surprising amounts of synergy with Khmer. The cornerstone of this is the Vaishya, which grants a population every time you send a trade route. Xerxes loves two things - trade and unique improvements. While the Baray is only one per settlement, securing a Unique City-State Improvement will supercharge Khmer Xerxes to crazy levels. Not only will you get enough gold to purchase the improvement with Xerxes ability, you’ll also get a migrant to place it anywhere you like, meaning you’re never limited by growth like you are with Han-Xerxes. As long as you’ve got cities to send trade routes to, you’re putting down more improvements. Bring Shisha Necklace and Suzerain around to give yourself more trade partners and improvements, and let all wealth flow to Angkor.
Just be careful about the Suvarnabhumi tradition, especially if using the Policy Card Yields mod. This works both ways, and the person receiving the trade route gets the culture, not the sender - so don’t get fooled by the policy card saying crazy amounts of culture. As Xerxes, that’s often mostly culture you’ll be giving to your allies which with all your trade routes could be a game-changing amount for a Deity AI.

The focus here is Benjamin’s Franklin’s Science on Production Buildings in Cities. Combined with Arogayasala, your Brickyard + Sawpit Quarters can outproduce your Libraries for science earned. He’s also a great user of Survarnabhumi - his extra Endeavours mean he’s excellent at making Allies to feed him Culture boosts, supporting his Science focus perfectly.

If you ever feel like playing Hatshepsut with someone who isn’t Egypt, Khmer are a great pick. Her Navigable River start bias is excellent for getting high value out of the Pithi Chrat Tradition - for Fishing Quays and Gardens in particular - and often lead to or spawn with Lake tiles for Tonle Sap value. If you want to get use out of her building boost, Khmer is a great choice. She also unlocks Abbasids by default, making a specialist focus with her just as potent as Confucius or Pachacuti.

Trung Trac loves tropical science civs, and Khmer is no exception. She’s probably the best user of the Dong Phaya Fai card, allowing her unparallelled movement in her tropical homelands. Combined with Trung Nhi’s unique promotion that gives combat strength in Tropical tiles, she can be a very scary neighbour. Set your science focus to beeline Yuthahathi early and unite the jungles for the Khmer Empire.

Yuthahathi is the strongest unit in Antiquity (which is why I didn’t feel the need to change them), being a cavalry unit with +5 Combat Strength. Charlemagne and Genghis can both add another +5 on top of that (Charlie in celebrations, Genghis with commanders) turning these into one-shot machines. Deity AI’s combat boost is +8 - you’re getting +10 for free. Once you utilize Dong Phaya Fai and Yuthahathi’s stealth on vegetated tiles to smartly use the terrain against the enemy, it’s over. The only downside is Yuthahathi’s -1 movement, but you can offset this with Commanders with the Initiative promotion (especially with Genghis, who gets faster commanders too). If you want a cavalry game that feels a little more tactical and terrain based, these guys are a fun pick.