The Freezer Event

An event where the temperature in a Minecraft world drops for some time (22 days for example)(the duration of this event shouldn't be too short but not too long either).

In cold biomes the player will freese if not wearing leather armor and extreme weather like blizzards will occur frequently. A one-block layer of powder snow will almost entirely cover the ground. Crops won't be able to grow if directly in contact with the cold weather. Lastly, a very cool feature would be that during this event, unique mobs like Mammoths, Saber Tooth Tigers etc will spawn only in the coldest biomes, only for the duration of the event, giving the player a reason to go there despite the harsh climate.

In other medium temeprature biomes like Plains etc light snowfall will occur usually, the water will freeze if not close to a light source like torches, a thin layer of snow will form on the gorund, and also mobs that typically spawn in snowy biomes like Polar Bears will start to spawn there (and the skeletons will be Strays). Also crops will grow slower

Hot biomes like Jungles and deserts won't be affected by this event.

Events like this will bring a lot of dynamic and variation in Minecraft and overall a cool addition. (events like this could replace the idea of seasons in Minecraft)