Damn nikkas came up with every possibility
I think it was either Lady Olenna. She didn't want Margaery marrying Joffrey anyway after what Sansa had said and the things they heard about him. Then again, Tywin threatened to put Loras on the Kingsguard, which forced her into agreeing to the wedding. Since Loras is the heir to Highgarden, why would she risk the Tyrell name dying?
Varys was looking uncomfortable from the jump. Maybe he didn't have direct involvement but had knowledge of what was about to go down.
I don't think Oberyn did it. He already has advantage over the Lannisters with Myrcella being in Dorne. His only real beef is with Tywin and the Mountain, even though he'll shyt on any Lannister given the chance
![pachaha :pachaha: :pachaha:](https://www.thecoli.com/styles/default/xenforo/smilies/pachah1.png)