Arena Block, also known as Arena Tile or simply Arena, is an unobtainable block encountered only during the Supreme Calamitas fight. It is almost completely indestructible, unable to be mined with any pickaxe or destroyed with any explosives, only able to be broken by the alt-fire of the Crystyl Crusher. It is spawned in a large box formation around the player immediately after they use the Eye of Extinction. This box varies in size depending on the difficulty mode, being 253x253 (inner available area 251x251) blocks in Normal Mode and Expert Mode, 189x189 (inner available area 187x187) blocks in Revengeance Mode, and 127x127 (inner available area 125x125) blocks in Death Mode and during the Boss Rush. Once either the player or Supreme Calamitas dies, Arena Blocks will break when they are within the vicinity of the player.
- Arena Block has no inventory item, existing only as a physical tile.
- Arena Blocks will not replace or overwrite any other blocks upon spawning, including Platforms and non-solid tiles such as Living Fire Block.
- The box can be escaped using teleportation items such as the Rod of Discord or going through gaps where the Arena Blocks are not spawned (as the former note states). However, doing so will cause Supreme Calamitas to enrage.
- While difficult to see due to the red shader applied during the fight, Arena Blocks emit red light which slowly oscillates between dim and vivid.