Tonberries are
broken in this game. They're one of the most fucked up, lethal incarnations of the beasties I've seen in FF in a long time.
Nothing in this game gives complete 100% safety from instant death save for a mastered Warding materia with a Subversion materia.
The amount of AP to get it mastered means its going to be a long, long time before that happens.
Cloud's Punisher counter can
sometimes block and counter the Chef Knife attack however, Gloom and Doom is another Instant Death move so you just either take it or hope you can guard against it.
FYI, in Hard Mode, Hell House will spew out 3 Tonberries during the fight against it.
Yeah.
Fuck tonberries in this game