Tatzlwurm gardener

Hm... As much as I want to Blame the Princesses for taking the Tatzelwurm's beloved Flower, logic tells me that the one who's truly at fault is Discord. He was never sick in the first place, acting like he was sick for the sole purpose of ruining Twilight and Cadence's day together just for his sick kicks. He knew of the Flower's location, which also means he was aware of the Tatzelwurm protecting it and knew that the Princesses would uproot it for the sake of helping a 'Friend'... I mean, from what I've seen so far (Tangled coming to mind), if you tell a Royal or their loyal soldiers that they need a petal from some incredibly rare flower, they'd uproot the whole thing and end up killing it to save or heal that friend/family member/Royalty they're loyal to.

So yeah, even though they didn't need to Uproot the flower, Discord was the one who started the whole thing in the first place and tried to play it off as a Lesson to try and get away with it once he revealed he was never sick in the first place! So the Tatzelwurm making him sick was Karma coming to bite him with Steel-Jawed teeth to the balls... And even then, he was getting off lightly.