In Cookie Clicker, when your on Christmas Season, you might see reindeer passing by! Click on them! They start out coming from the left to the right and once there gone from the right, you have to wait a while to see them again and catch them!
How to find Seasons
To find season, press Legacy and yes. Click on the circle with a cookie that looks like a tree. Then come back to the world and you'll find it under Upgrades and press on it. Now you have 24 hours to be on Christmas season with your reindeer.