The Immortal Thor

This deck is all about the mantra "Threat prevented is threat removed." Keep Thor in hero form with Energy Barrier, Preemptive Strike, and Second Wind, use Black Widow to prevent any really nasty encounter cards (like Advance, Shadow of the Past or side schemes), and rely on your other allies to remove threat. You should be keeping allies like Heimdall or Lady Sif in play indefinitely with Med Team and First Aid to ensure efficient threat removal. Protection also provides a lot of energy resources for Lightning Strike.

You should never be flipping to alter-ego form unless it's absolutely necessary or you can guarantee yourself a safe villain phase. It requires a very unique play style, but I've defeated every scenario on Expert with this deck, including Ultron with Legions of Hydra and Mutagen Formula with A Mess of Things.