Defeating the enemy with spies

[caravel]

Low level spies, when mass produced, make EXCELLENT cannon fodder for border forts, when using assasins, as the border forts target the spies first. If you need to assasinate someone in "safe ground" toss some spies (I think the lowest limit is 4) along with your assasins. The spies will get fried, but the assasins will slip through.

(I destroyed the Castilian royal line like that playing as the almohads)

Another "assasination" you can carry out is slipping in many ranged, fast units in the battlefield, and going for the enemy king, then withdrawing against the overwhelming odds.

(This worked just fine playing as Byzantium to supress a Turk reemergence during an Egyptian civil war)

I'm not sure about that method. The border fort will catch and kill the majority of any number of 0 valour spies/assassins you can throw at it. If you send 20 and get one in there alive, you'll be lucky and the BF will get him next year anyway unless you pull him out. Of course storming a lot of agents at a target increases your chances considerably but sending spies that cannot actually perform the mission, assassination, seems to be largely pointless. There is no limit as to how many agents the border fort can catch in one turn and it doesn't become less effective as it catches them.