What does the UP button do?

I was playing Zane last night, my main character, and I happened to hit the up button and a grid appeared. I was farming Graveward and he was outlined in kind of a grid with a red center, like a reticle, that seemed to try and line up with the critical spot on his chest. I haven’t found this referenced anywhere. Anybody know?

Thanks.

NPMedic

I’m not sure what the default up button is anymore, but maybe you tagged him?

It’s the marking option like enemy, crate, place etc. Useful in coop, useless in solo.