Minecraft Forums

You can make a soul sand block (sort of) with this following method:

public AxisAlignedBB getCollisionBoundingBoxFromPool(World p_149668_1_, int p_149668_2_, int p_149668_3_, int p_149668_4_)
{
float f = 0.125F;
return AxisAlignedBB.getAABBPool().getAABB((double)p_149668_2_, (double)p_149668_3_, (double)p_149668_4_, (double)(p_149668_2_ + 1), (double)((float)(p_149668_3_ + 1) - f), (double)(p_149668_4_ + 1));
}

public void onEntityCollidedWithBlock(World p_149670_1_, int p_149670_2_, int p_149670_3_, int p_149670_4_, Entity p_149670_5_)
{
p_149670_5_.motionX *= 0.4D; //This is the Speed(0.4 is soulsand speed)
p_149670_5_.motionZ *= 0.4D; //This is the Speed
}
}

Hope you enjoy!