You choose which one of the 150 point characters to be pacted.

thanks for your answer

I believe highfathers controller chooses who gets the pact when there are two characters with the highest point value

Hi, Another question :

My opponent plays a team base. I activate the pact.
My opponent only has one character on the map, he can attack.
But if he use the solo abaility, my opponent has more then one character on the map.
If Highfather and the team base has not taken damage, the team base can attack ?

No. Once the Pact is broken, it is gone for good. There is no turning it back on so to speak.