(define Ω (let ([w (lambda (f) (f f))]) (w w)))

The difference between an early Fire Hazard and an early Mountebank is that getting Fire Hazarded makes it harder to defend against future Fire Hazards (by quite a bit, when you're adding two dead cards to a thin deck with (say) only one action in it so far), while getting Mountebanked makes it easier to defend against future Mountebanks. But I could believe that this difference is not very significant in practice.