First, he's a very solid addition to the many blue-oriented, artifact-love archetypes that see a ton of play at the kitchen table
Lifegain is a popular mechanic among Commander players (at least very much among the players that I know), and a simple 4-drop that not only shuts off all lifegain but reverses it into life loss seems like an extremely powerful effect to me
Cycling is a mechanic that's incredibly difficult to play around since you can't counter or do anything to stop the ability other than parity-breaking stax pieces like Narset, Parter of Veils
Thankfully, there are quite a few cards with more than one card type to feed Winter
Felix Five-Boots | Illustration by Chris Rahn Hello planeswalkers
Pillow fort cards look to mitigate all incoming damage by either gaining life, incentivizing opponents to attack each other, or just flatly preventing the damage from happening