Here's what rhymes with invulnerable.

Consider these alternatives

invincible / principle powerless / flowerless indistinguishable / distinguishable inconceivable / feasible unsuited / routed immobile / total immaterial / material superfluous / thus unrecognizable / advisable unrecognisable / recognisable obliterate / late superhuman / human incapable / capable unemployable / employable omnipresent / present contrarily / necessarily