Question about how we can play this. I have a potion of heroism in hand. My buddy, who's at my location, encounters Owlbeartross. Can I play the potion of heroism at this point? Or would I have had to play it prior to him exploring and starting the encounter?
If you buddy is making a check you can display it. Or you can display it outside of the encounter. Either one is a suitable way to play it. See this similar thread about the spell Rage. Granted, Rage is more limited in the type of check your buddy has to be making, but mechanically they work the same way.
You can also see this thread about Strength which was confirmed by Vic here.