What unique tech gets the craziest when researched specifically 3 times?

I'd say that it could be Stirrups, Double Crossbow, Perfusion, Steppe Husbandry, Drill or Mahouts.

So it's:

• Cavalry that attack multiple times a second
• Scorps and Ballista Elephantos that fire 4 projectiles
• Insta-create infantry
• Insta-create Steppe Lancer, Hussar and Cav archer
• Siege that move faster than Hussars
• War Elephantos that run at the speed of Paladins

Any more crazy Unique techs?