the Jester
Legend
The mushroom patch can easily be fixed to be terrain - change "characters" to "anything".
This allows both sides to utilise it.
As stated previously terrain features are just there and provide something that is impartial - Blood Rock for example.
A Trap/Hazzard is solely there for the purpose of hurting the characters.
D
To reiterate:
The mushrooms are in an encounter with a solo monster only. The monster resists 20 acid. The mushrooms are totally stacked against the pcs.
I suppose if anyone had a "lose all resistances until EOT" or something power, the monster might take a little damage from them... but that's a reach.