That's a good question. Try one of these:
formidable
epic fail
characteristic, particular, exact, special
One way: Fail - Fall - Fill - Pill - Pile - Pals - Pass Another: fail > pail > pall > pals > pass
Must is that you have to do it no matter what. For example, you must do the test or you will fail.
Indeed, the word "guaranteed" is spelt correctly.
The base word for "failure" is "fail."
fail - fail(s), fail(ed), fail(ing), fail(le), fail(ure)
ed
The likely word is "guaranteed" (assured, or warrantied).
pass
Just what I need; another competitor. This competitor will fail just as miserably as our previous competitors!