If you become Salamence, or anything else that always has Intimidate, the jig is up immediately. I'd copy something that has weaknesses where the Illusion Pokémon has strengths. Bullet Punch aside, Gengar's not a bad choice. If you're lucky, you'll be hit by a Ghost, Dark, or Psychic attack.
Bear in mind here that I'm mostly thinking about double battles, where that one free turn can be huge. Even if the opponent figures it out after you take little to no damage from its attack, you may have just used that opportunity to turn the tide of battle.
Although, honestly, I'm more excited about the prospect of Ninetales getting Illusion and looking like a Grass-type, giving it the opportunity to use any number of support moves like Safeguard, Imprison, Nasty Plot, etc.