Does Twitch's Poison and Deathfire Touch stack?

Well... yes, they can both be on the same target at once, but Twitch has only 1 spell that can apply it and only for 2 seconds (his E). It wouldn't be wise to use DFT on Twitch. Even Fervor would do more for him.

pls answer

I use DFT on Twitch all the time. It's awesome. Considering it adds a lot of "dot" damage after you get a few autos in and press E to chunk them. You'd be surprised at how effective it is in lane vs fervor or other keystones. Teamfights... once you get hurricane or land your ult on multiple targets, you get all that DOT damage on EVERYONE you hit.

It's great, try it.

I haven't fully tested it or been keen enough to watch for it, but it considering his passive is an ability, it may also proc there for 1 second. :)