If it's a Tyrell, it's stupid. It's super not Oberyn, that's even stupider. There's an outside chance it was Tywin. He does have motive, but he also has anti-motive. He did once say he's going to get the Tyrells back, but this only kinda sorta weaksauces that. He also could have purpose to get Joff away for other reasons, but not doing so is still probably better

I just wonder if this will spell doom for Tyrion. I can't imagine GRRM would have killed him this early, but maybe. Somebody is probably going to die, but I imagine that can be avoided, since the only person who loved Joff was Cersei. Other than that, Tommen can be the new king, with Tywin as regent, and things would go on like normal. In that respect, it makes it being Littlefinger seem a little pointless. This shouldn't create much chaos at all, since Tywin was always the one with the meaningful allegiances. Come to think of it, if it's LF, his motive must have been to keep a royal baby from being made and keep the Tyrells out of things.

I guess it probably is LF and the poison was in the pie, but red herrings have been set up, and I never like those if they're not logistically sound