If you're playing doubles or triples, Trick-or-Treating a Normal-type will either wall Aegislash completely or make it even more predictable depending on its set.
Outside of that very specific instance, try what others have stated. If you're feeling like pressing your luck, try a Protean Kecleon. --- "In the beginning, the Universe was created. This has made a lot of people very angry and been widely regarded as a bad move." -Douglas Adams