can I create a metric (mixpanel) where it counts as 1 for each 2 times it gets triggered?

Yes, I think you can do that with a custom aggregation. Instead of

sum(values)

, you can do something like (

Math.floor(sum(values)/2)

).

I was about to test that, I first though this

Math.floor(values.length/2)

would work

Yeah, if the value is always 1 each time that should do the same thing.