Im on a field space along with an object and the pool of life. My opponent lands there to battle and I respond by using invisibility potion. Can he then choose to encounter the cards on the space instead since we didn't battle?

I don't think so. A character can EITHER encounter a character OR the space. Not both. Therefore, since he stated his intention to do battle with you he clearly was encountering a character even though you were able to cast the spell to avoid battle. His turn simply ends at that point.

That's what I told him. He believes that by evading him he hasn't yet encountered me so is free to encounter the space instead. Anyone else wanna chime in. We've got 10 bucks riding on this. Lol

Once you make a choice you have to stick with it. Gonna roll for the mystic, oh I turned into a toad, Nevermind I will see the alchemist instead. Don't think so!