Update: removed an observatory and added Lacuna Entity. Provides more removal in a body. Removed Ruby core in place of Shrine of the Dragonlord. Replaced Ruby and provides Water and Air threshold.
Mephistopheles the Magician
A Magician build running Air as the primary element with two genuine secondary element payoffs rather than a splash: Water carries Lilith, 2x Lord of Lies, and Great Old One, while Fire carries Balor, Asmodeus, and Grigori Rasputin. Sitting on top of all that is a deliberate cluster of threshold-bypass tools including the Cores, Wiccan Tools, Four Waters of Paradise, Den of Evil, and Mephistopheles himself and De Vermis Mysteriis, so the three biggest bombs are never permanently stuck in a hand that never draws the right sites.
Early turns lean on Clairvoyant and Screamer for tempo and smoothing (if cemetery minions are available), with Rasputin as a real but not guaranteed turn-two play. The midgame is where Bane of Aventis, Lord of Fear, Lord of Lies, and Mephistopheles start doing the actual work, with Toolbox coming online as soon as the curve is being cast on time, since three copies means the Collection should be reachable most games. Great Old One and Doom of Dilmun close it out, backed by whichever threshold-bypass piece is still in hand if Water or Fire never fully assembled. Every minion in the deck besides Clairvoyant is Evil, which lets a spent or dying ally feed Rasputin's recursion, and Black Mass doubles as a tutor for three evil minions.
The mulligan here is close to free, so use it. Bottom sites before anything else, then an un-castable top-end card with no path to its mana, then a redundant cheap duplicate if the curve needs smoothing more than the flood does. A keepable seven needs two or three sites including an Air source and one castable play before turn four; it doesn't need a full curve to be worth keeping.
A few cuts are worth knowing if you're comparing this list to earlier versions I have listed below. Renatus Trueblood is a strictly worse Daperyll Vampire and was cut outright. Draconian Bonekite's Air-3 cost too much relative to what it did. Young Master Damion and Nosferatu were low powered bodies replaced by Screamer and Rasputin. A second Chaos Twister became the third Toolbox once Collection access proved more valuable than a redundant removal copy.
Twenty-two sites is on the higher end for this list, and if testing shows the deck flooding more than it should, the fix is to cut one Den of Evil and one Observatory rather than touching anything in the Water or Fire suite. Both are pure Air, both already run in multiples, and Air has enough depth elsewhere to absorb losing two copies without affecting the threshold math this list was built around. We would replace those two sites with 2x Stygian Archers.
Previous Versions:
Lords of Mephisto: https://curiosa.io/decks/cmlpal8oa009m04jvklxaofvn
Lords of Corruption: https://curiosa.io/decks/cmn9vtiyw00k304jvtcn268e1
4th Place Spellslinger: https://curiosa.io/decks/cmrrv12uq00030aky0clmoize