The soul seer is a useful redstone component. When powered or clicked, it make mobs glow in a 24 block radius. The type of mob is based on the block beneath the soul seer. A full list of these blocks can be found in this guide.
It can also be used as a mob detector. The comparator output of the block represents the number of mobs it highlights. If you placed tinted glass on top, it will only give comparator output and will not make any mobs glow.

It’s crafted with sculk, making it a useful reward for looting the deep dark.
History
| 1.6.3 | Beta 1 | * | Sulfur cubes can now be highlighted using a soul seer with sulfur beneath it. |
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| 1.6.1 | * | New Mounts of Mayhem mobs can be highlighted by the soul seer:
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| 1.4.1 | * | The gobblerift, nether reactor, and soul seer now have emissive textures | |
| 1.3.6 | * | Soul seers can now make breezes glow using chiseled tuff | |
| 1.3.4 | * | Armadillos can now be detected by the soul seer using an acacia log | |
| 1.3.2 | + | You can now “pick block” positional anchors, soul seers, soul conductors, and pottery tables by control+middle-clicking them | |
| 1.3.0 | * | The soul seer has been entirely reworked into a redstone component It no longer requires glowstone dust as fuel
When clicked or powered, it makes mobs glow based on the block placed beneath it
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| 1.1.0 | Beta 4 | * | The soul seer’s range has been nerfed from 48 blocks down to 24 blocks |
| Beta 3 | * | The soul seer has generally been rebalanced to make it less costly and more effective.
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| Beta 1 | * | The soul seer is now crafted with deepslate and a single echo shard, rather than soul sand It now triggers observers when activated and deactivated It also has an amazing new texture, shown above | |
| 1.0.0 | + | A new magic block, made with soul soil, an ender eye, glowstone dust, and gold. When clicked with glowstone dust, it consumes the dust and makes all entities within 24 blocks glow. | |