Prepped or geared invoker can really screw with a warrior.

Dispel magic immediately to strip stoneskin, protection, fly. Grease to screw up potion use, web to drop dex and if lucky to hinder weapons. After that proceed with usual spells, Iceneedles is a good choice as many people do not gear against it (heavy, strong material full face helm being the most important), plus Mirto has no resist_physical unlike a giant. It is also relatively good against high svspell, as compared to spells like fireball/forked lightning which are hindered by good svspell. Immolation is not really as useful against warriors as it is against casters, but it is still a good spell if you can get the burning maledict on him. If he is fighting near the right sort of terrain, a quicksand will certainly seal the kill along with web, grease, iceneedles (and give <warrior> raft).