Treasure Chests are prizes awarded in Magic Online for strong finishes in Magic Constructed Leagues as well as Vintage Daily Events.
Like all League prizes on Magic Online, they are added to the player's collection once their course through the League is complete. Treasure Chests were announced in September 2016. 
You're guaranteed to get at least one of these virtual items in a Treasure Chest:
- Curated Cards — These are cards selected by Magic R&D for their desirability in Magic Online.
- Modern-Set Rares and Mythic Rares — Any regular rare or mythic rare in a set that's legal in Modern can show up in Treasure Chests.
- Play Points — You can receive different quantities of Play Points in Treasure Chests.
Most of the time, you'll also get two Standard-legal commons or uncommons. But sometimes one or both of them will be replaced with either a curated card or a Modern-set rare or mythic rare.
Magic: The Gathering sets