Winter, Misanthropic Guide

Ward {2}
At the beginning of your upkeep, each player draws two cards.
Delirium — As long as there are four or more card types among cards in your graveyard, each opponent's maximum hand size is equal to seven minus the number of those card types.

Duskmourn: House of Horror Promos

Duskmourn: House of Horror

A player's maximum hand size is checked only during the cleanup step of their turn. At other times, they may have more cards in hand than their maximum hand size.

If multiple effects modify a player's hand size, apply them in timestamp order. For example, if you put Winter onto the battlefield and then your opponent plays Reliquary Tower (a land with "You have no maximum hand size"), that opponent would have no maximum hand size no matter when you started having delirium. However, if the permanents entered in the opposite order, that opponent's maximum hand size would be seven minus the number of card types among cards in your graveyard if you had delirium. At any time you didn't have delirium, they would have no maximum hand size.