|Max Life||2 hits to destroy with Pwnhammer|
Demon Altars are naturally-occurring crafting stations found mainly in and around Chasms in The Corruption, caves in The Crimson (called Crimson Altars), and more rarely in other areas Underground. They are used to craft boss-summoning items and the Night's Edge. Altars emit some light, making them easy to spot. They cannot be freed, picked up, placed, or crafted. After a world enters Hardmode, they can be destroyed, but attempting to hit them with a hammer before that causes the player to lose half their health, and the Altar will not be affected. Whether the Altar is purple or red depends on whether it is a corruption or crimson world.
After the Wall of Flesh has been defeated in a world, Altars can be destroyed with the Pwnhammer or any superior hammer. Each destroyed Altar causes one type of Hardmode ore to appear in the world, with the appropriate message displaying in the player's chat: "Your world has been blessed with (ore)". If a player attempts to destroy the altar with a lesser hammer, or in a world in which the Wall of Flesh is not yet defeated, the altar will be unaffected and the player will lose half their current health, as stated above.
Smashing Altars always results in Cobalt (Palladium), then Mythril (Orichalcum), then Adamantite (Titanium) ore being generated in respective order. The Altar resets the sequence after Adamantite/Titanium, and continues to cause additional Hardmode ore deposits, thus increasing the distribution of the Hardmode ores with each successive time the player smashes an Altar. Each time an Altar is destroyed, 1-3 Wraiths spawn, regardless of the time of day. When destroying multiple Altars in rapid succession, the resulting Wraith swarm may become difficult to deal with.
Which ores are generated is not determined until you smash an Altar. For example, it is not determined which ore your world has, cobalt or palladium, until the first altar has been smashed. The same goes for Mythril/Orichalcum with the second altar, and Adamantite/Titanium for the third. But once the first three altars are destroyed, the sequence is permanently set. If you get Palladium, Mythril, and Titanium, with your first three altars, your world will always produce those and only those when altars are destroyed.
In addition to spawning new ore, a small patch of Corruption or Crimson will be spawned at a random location on the map. Smashing a large number of Demon Altars will often result in a chaotic world splotched with corrupted/crimson and hallowed areas underground.
 Used to craft
 Hardmode ore spawns
- Small maps:
- Medium maps:
- Large maps:
- Altars are not used to craft hardmode boss summoners.
- Altars cannot be collected as items.
- Altars generate less and less new ores as more are destroyed. The second set of altars create 1/2 as much ore as the first set, the 3rd set creates 1/3 as much as the first, and so on.
- Cobalt(Palladium) is roughly twice as common as Adamantite(Titanium), with Mythril(Orichalcum) halfway between.
- Each time an Altar is destroyed, there is a 66% chance that a single random tile in the rock layer will be converted. Only stone blocks can be converted, and they will be converted to ebonstone, crimstone or pearlstone. This will grow to become a new underground Hallow, Crimson or Corruption if given enough time.
- For players that dislike the thought of a random block in the world turning to ebonstone, crimstone or pearlstone, try breaking Altars in an other world, of course, you would have to have killed the Wall of Flesh.
- Altars encountered outside of the Corruption/Crimson on a given map will always be found at a depth of around zero feet.
- Attempting to destroy an Altar with a Pwnhammer before killing the Wall of Flesh will hurt you just like a regular hammer.
- Players about to enter Hardmode may benefit by mining paths to several known Altars beforehand, as navigating Hardmode Corruption/Crimson is dangerous at first.
- If you destroy every Altar in a world, it then becomes impossible to use them for crafting (at least within that world). Leaving one that's easily accessible in your world might be wise, there is usually one in the nearest cave from spawn at underground level. Alternatively, you can also create a new world and use Altars there for crafting.
- Players should not destroy all the altars just for ore as the amount of ore spawned reduces for every 3 destroyed altars. And the altar, when smashed, will spawn a tile of corruption or hallow, which will soon grow into a new corruption or hallow.
- 188.8.131.52: Fixed the problem with altars/pots/chests spawning in bugged conditions.
- 1.2.3: Fixed dying by demon altar having no message. Crimson Altar now shows up when you hover over it on the map.
- 1.2: Worlds which have the Crimson instead of the Corruption will have Demon Altars replaced with Crimson Altars.
- 1.1: When smashed with a Pwnhammer or a Drax during Hardmode, either Cobalt, Mythril, or Adamantite will be spawned in the world. Also, it now has a chance to summon a few wraiths and create additional Underground Corruption or Hallow spreading point somewhere in the world when smashed.
- Pre-Release: Introduced.