Poison the well and wellspring seem to not stack. Would be good to have this listed on the card.

Indeed. I’ll have a look at this, and either try to make them stack when that’s fun or try to adjust card text to reflect what’s happening.

Thank you. If there are multiple cards were this is the case, a special text to indicate would be nice. Similiar to "causes Burning".

"Limited effect" .. there's a better name but that's the idea

I think only venomous bite and healing rain stack. And volley, too (but only 1 turn). Stacking rain and bite is my favorite strategy :)