Soul Sand is a brown-grey dirt-type block with sad, pixelated faces on it.
Soul Sand (A.K.A. Hell Sand or Slow Sand) is a Block that was added in Update 0.12.1. It generates naturally in the Nether.
Soul Sand is an agent bought for 25 Monkey Money. It can only be placed on the track, and only on land. It slows all bloons that go over it by 20% for the rest of the game. It slows down S.T.E.V.E.s even more. The Pro version is unlocked after 50 uses (1250 MM total) and puts ice under the Soul Sand, so it slows the bloons by 35% and even more for S.T.E.V.E.! The Epic Version is unlocked after 50 MORE uses (1250 more MM, 2500 total) and is now a 1-way door. The bloons take 3 damage trying to get through, which takes 3 seconds, though blimps fly over the door. (The slowing still works for all Bloons)