Lipogram: a composition in which the writer systematically omits a certain letter or letters of the alphabet.
Pick your favorite form, or even free verse, and write a lipogram. Or take a poem you have already written and adapt it.
This sounds easy, I’ll just leave out ‘x’, but no my friends I add a further restriction:
The letter(s) you leave out must be chosen from the following list: a, s, d, f, e, r, t, c,b, n, i, o, or m.
Here is a novel written entirely without the use of the letter ‘e’ for inspiration: Gadsby