This one was requested yesterday by someone, I completely forgot who though.
You wake up one day and realize the Alicorn Amulet is around your neck. You also have a horn.
How do you use your newfound abilities? Can you resist the pull and use your new highest level unicorn powers for good? Or do you take over the world and force everyone to build statues in your honor? We can probably assume that someone who is already susceptible to greed, narcissism, and evil will be inherently weaker to it's influences.
Hard Mode: If your plan involves Equestrians, the amulet has limited your power to only summon and communicate with ponies you genuinely dislike!