Thought this might be helpful for aspiring scenario/mod creators or anyone for that matter. Well, I had been implementing my own personal Civilization, but I ran into the problem of upgrading a regular unit to my UU. So I did a little logic work and found how Civ knows what a unit upgrades to. What Civ does is work in a Yes/No fashion (or so I've found) when finding the right unit to upgrade to. I'm going to use the Horseman->Knight example. When you upgrade a Horseman to Knight, you get a Knight. When you have a UU that replaces the Knight, you get that unit. This is the path for upgrading a Horseman: Horseman->Mounted Warrior->(Three-Man Chariot)->Knight->(Keshik)->(Ansar Warrior)->Rider->Samurai->War Elephant->Cavalry. For this example, I'll say I'm playing as the Chinese and have a Horseman to upgrade. I click the Upgrade button, and Civ then checks to see if I get the Knight, if 'NO' then it goes to Keshik, and so forth. Now I want to add a UU replacement for my Civ. Let's say I want a Lancer. Now, I have to go to War Elephant and change it's upgrade path to Lancer. Then I have to make Lancer upgrade to Cavalry, like this: Horseman->Mounted Warrior->(Three-Man Chariot)->Knight->(Keshik)->(Ansar Warrior)->Rider->Samurai->War Elephant->Lancer->Cavalry. Actually, Lancer can go anywhere after Knight and before Cavalry, as long as you don't break the chain. --- Now, if you add a unit that replaces the Horseman, You can either set it to upgrade to the Horseman, or put it after the Mounted Warrior (Three-Man Chariot in C3C) and have it upgrade to Knight. I hope that helps anyone who may need it. If anyone needs a pic or two just ask and I can get one for you. Note: Parenthesis enclose units in C3C or PTW.