Deadly
Paxillus syndrome
An immune reaction rather than a toxin as such
Onset after the meal
1 to 3 hours, but only after previous meals have sensitised you
Inside six hours, which is the reassuring side of the line, with one qualification: a mixed wild meal can produce an early reaction that hides a late one.
Attacks
Red blood cells, through the immune system
What it does
Vomiting and diarrhoea, then pallor, jaundice, dark urine and collapse as antibodies destroy the eater's own red cells.
How it runs
Can progress to acute kidney failure and shock. Deaths are documented.
Treatment
Hospital. Steroids, transfusion and plasma exchange. Not something any home remedy touches.
The catch
Unique and genuinely counterintuitive: the mushroom must be eaten repeatedly to become dangerous. Years of eating it without trouble is what sets the reaction up, so a long safe history is a risk factor rather than reassurance.
Species that cause it
This is reference material, not clinical guidance and not a substitute for a poison centre. If somebody is unwell after eating a wild mushroom, call one now, tell them the interval between the meal and the first symptom, and keep an uncooked specimen.