This page or section includes possible gameplay spoilers or secrets. Tread carefully.
Great Treasure Chests are rare chest variants with far better rewards than the regular Treasure Chests. They have a 1/1000 chance to spawn in place of a regular treasure chest.
When generating a new area, there are specific locations that can spawn an Extra Max Health or a chest. For each of these places, there's only a 2/5 chance it spawns a chest. If that roll succeeds, 1/10 chest spawns instead spawn a Mimic, and only 1/1,000 spawn a great chest.
As a result, the probability of getting a great treasure chest from any given possible heart spawn location is 9/25,000 (0.036% or 1/2,777).
There are also some guaranteed chest locations which can spawn in the Mines (see the Gallery below) which have a 1/2000 chance to spawn as a Great Treasure Chest instead. Having the Curse of Greed active will cause them to have a 1/50 chance.
Upon opening, it spawns items according to the following table.
Bold is the individual probability for each roll, italics is the overall probability of the final outcome relative to all other outcomes. 
|30%||Spawn 3 Potions|
|3%||It rains Gold nuggets|
|1%||A Tier 3-6 Wand|
|21%||A Health Pickup|
|39%||Roll this entire loot table twice.|
|1%||Roll this entire loot table 3 times.|
|1/100,000||Spawns the Sampo. Cannot be selected if either of the "roll again" options above have been picked.|
When the chest rolls the "roll again" options repeatedly and finally stops, the potions are selected at the end of the script when it actually spawns the entities. This is why, no matter how many times it loops on itself, it only creates up to 3 different potions each time you open it. As a result, when it repeatedly rolls the random potion options, it creates a large cluster of the same few potions rather than a more random selection.
The wands get much more complex code, so while rolling the same variation of a wand repeatedly is unlikely, it is still possible.
- Be very careful as these chests have a high chance of pulling from the random material pool, which can rarely spawn Creepy Liquid (among many other odd or dangerous materials), potentially ending a run very shortly thereafter.
- If you spawn a Great Treasure Chest via The End Of Everything, focus on killing the Jättimato; if they destroy the chest, it may open and break the potentially very hazardous potions contained inside.
- Combined rolls don't take into account the chance that they are rolled by thrice or twice or more openings as this would get a lot more complicated as they can then roll the twice or thrice roll again.
- Tiers marked with a + pull from the
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- The "roll multiple" possibilities in the loot table can roll themselves recursively. It's possible for the chest to open three times, only for it to select roll three times or roll two times repeatedly, causing these chests to rarely explode with items until running out of extra rolls.