I doubt Undertaker wouldn't want to get in the ring with Lesnar because he's an MMA guy who could "legit kill him" if he wanted to

. Even a guy like Lesnar who isn't exactly passionate about the business would have far too much respect for a guy like Undertaker in the ring to try anything. Would seriously

if they do end up facing each other, but I'm definitely thinking Punk is the guy Undertaker is going with this. As for heat between the two, not surprising that its there as Undertaker was one of THE guys to really make Lesnar (Rock dropping the belt was the other main one), and then Lesnar just up and left after 2 years.
And lets not forget there is apparently some heat between Undertaker and Punk going back to 09 (based around clothes if the dirtsheets are to be believed

. IMO its probably down to Punk's attitude as he's well known for being a bit of a prick lol).