This is a task that'll bring you back a great profit if successful but may also end you up with heavy loss even your life. I have been thinking whether there is one word or a phrase or some self invented compound word to substitute for the long attributive clause.
I have found a sentence:
The cave that you fear to enter holds the treasure that you seek.
So how about : This is a treasure-holding-but-you-fear-to-enter-cave task ??
Best Answer
As one commenter noted:
Therefore, I am surprised that no one has mentioned "high-stakes". From e.g. here: