Looking for clarification on track and kill.

My friend thought that when you picked a character it would include all of those characters on an opposing force.

I disagreed and believe it only works for the specific clix piece picked.

Who is correct?

It's only the chosen character. I don't know where your friend got "Entire force" from, because the trait mentions only "That character" multiple times.

OK that's what I thought.

He wasn't saying entire force. He was saying all of that character on the force.

Like if I had three of the same Cyclops, a Jean Grey and a Beast. If he chooses a Cyclops he believed it would work for all/any of them.

Oh, no. I don't believe it would work like that at all. If you have multiples of a named character on a force, they all still count as distinct, different characters. Therefore, if Wolverine's opponent has two Sabretooths, and he chooses Sabretooth, Wolverine could only Track and Kill the specific Sabretooth he chose.

Each piece is it's own character.
A character is a specific individual game piece.

Doesn't matter how many there are that share the same name, doesn't matter if they share the same set number.
They are all their own character.

If that effect was supposed to work the way your friend is trying to make it work then it would say "if a character with that name..." or something of that sort.