Best Combined UUs?

By combined UUs I mean one UU upgraded into another UU. Lets say there's a team of 2 people what are the best combined UUs of one UU upgrading into another?
Here are some epic ones I thought of.
Janissary-Carolean, combined with some medic units and double healing from FoY I would say perpetual motion has been achieved. Even though the FoY is very rare and likely not to be get this UU is still a very capable unit combo.
Jaguar-Legion, a legion that heals on kills and moves through forest/jungles with no penalty would be next to unstoppable!
Jaguar-Janissary, If the heal on kill stacks this would be quite hard to kill.
Slinger-Chu-Ko-Nu, would be quite hard to kill with melee units and the following turn the melee units would get blasted!

I've experienced Minutemen upgraded in to Caroleans. Can't beat that to be honest.

Jaguar->Spearman via ruins->Sepahi

5 move through forest and jungle, extra sight, heal on kill, no-movement plunder, they're like special forces. Extremely mobile and hard to kill.

Pathfinder to Longbowmen/Chuks would be amazing. Or maybe scout to slinger to Longbowmen/chuks

Friend of mine had a Kris Swordsman from a CS (with Recruitment promotion) upgrade to a Minuteman once.

horse archer->keshik->hussar

Pathfinder-> cb-> longbowman
pathfinder-> CB-> chu ko nu
both pathfinder upgraded through ruins^^

How about a classic jag+mohawk? This would be amazing in vanilla when swords were good (i actually tried it in hotseat once...)