I’ve read many suggesting that civilizations that have unit stat bonuses could have unique skins for them (this thread being the first where I’ve seen this proposed: (only) constructive feedback on AoE II RoR), as a way to add more flavor and uniqueness to their identities without messing with the classic gameplay by adding Unique Units. So, here’s a compilation I made with references of what these units would look like, according to each civilization’s bonuses!
Assyrians
Bowman shot 10% faster.
Babylonians
Chariots have +1 piercing armor.
(this one is actually an Assyrian)
Carthaginians
Academy and Elephant units have +25% HP.
Camel Rider have +15 HP
(I couldn’t find any images of a Carthaginian camel rider, but I think, ironically, this one is Roman

Fire Galley have +25 attack.
If I had to choose one, I would choose the Elephant, as it is the most iconic, thanks to Hannibal!
Choson
Axeman and Short/ Broad/ Long Swordsman and Legion have +5/ +15/ +20/ +60/ +80 HP.
Egyptians
Chariot units have +33% HP.
Priests have +3 Range.
Phoenicians
Catapult Trireme and Juggernaut shoot 33% faster.
Greeks
Academy units move 30% faster and costs -20%.
Hittytes
All bowman +1 attack.
Warships (except Fire Galley) +2 range in Tool Age, +3 range in Bronze/ Iron Age.

(I couldn’t find anything about Hittyte warships, but I’m ironically adding these Egyptian ones).
Lac Viet
Archery Range units +2 armor.
(I could barely find this one, and I don’t know if the period or even the civ is correct

Macedonians
Academy units +1 Pierce armor in Bronze Age, +2 in Iron Age.
Minoans
Composite Bowman +2 Range.

Palmyrans
Camel Rider move 25% faster.
Persians
Elephant Units move 25% faster.
Scout Ship line shoot 18/ 25/ 33% faster in Tool/ Bronze/ Iron Age.
(the trireme being rammed is the Persian one).
Romans
Swordsman attack 50% faster.
https://cdn.thinglink.me/api/image/581954712534777858/1024/10/scaletowidth/0/0/1/1/false/true?wait=true
Shang
Cavalry line attacks 10% faster.
(I don’t know if the period is correct or even if they are all actually Chinese, sorry).
Sumerians
Camel Rider +1 pierce armor.
Yamato
Ships +20% HP.
Unfortunately, I couldn’t find any pictures about what ancient Japanese ships looked like, so here’s how their cavalryman dressed, as all their Cavalry and Cavalry Archers cost -15%.
I chose not to consider siege engine-related bonuses, as many of the civilizations with siege bonuses have probably never used catapults or ballistae, and those that have used them are well served by the models already present in the game. I think they should add Rams in the future so the Sumerians and others can have unique models for them.
I also ignored bonuses off unit costs, as this doesn’t reflect any bonuses to strength, speed, or range that effectively make units more advantageous. Since I didn’t find anything about the Yamato ships, I added a cavalry example, although it was related to a discount bonus.
If you find better examples of the units here, please post them in the comments!