It’s Blue Eyes White Dragon, baby! One of Yugioh’s coolest cards, even if the power creep has rendered it almost as outdated and obsolete as Piccolo.
 
Silver normally uses magic to physically transform himself into this or that, and then makes a costume to go with the form, but Ponyville’s Nightmare Night frowns upon using magic to “Cheat” in that way, so Silver constructed this costume himself! It’s made of real metal plates, with a complex system of joints used to ensure near-perfect freedom of movement within the costume. It leaves the user’s forehooves free as a design choice, while covering his back hooves. The tail can move freely in any direction, but upon seeing everypony else’s costume and realizing that he was taking this costume thing WAY too seriously, he decided to keep it stuck out and bent like this, so it would look less professionally-made. His slimesuit, Suit, hangs out in the tail region for storage, and she’s turned green because she just wanted to observe this year’s Nightmare Night celebrations, and take part in it properly next year. If anypony asks, she’s “Dressed up as” Skurd from Ben 10, and will emerge only if she has to.