when i was designing this me and my lovev had a discussion about that middle shroom. nintendo itself says its a "poison" shroom and that's what it's always refered to as.
but anyone that's played mario (especcialy the lost levels) they'll know that poisen = instant death. theres no walking around slowly losing health, or turning green and flashing liek in other games, you just touch the shroom and perish
and thus, in my stiching We called it the death shroom, as really, that's what it is