If it's counted as an item (if people consider Terraria like Minecraft and separate blocks into a different category), that would be silt. It's an ugly grey colour, so you can hardly use it in building things, and falls if you want to build sky bridges or houses, not to mention that IT KILLS YOU. Making makeshift towers out of it when you don't have the grappling hooks to reach high places is pretty dumb; if you want your little platform to go sideways, you'll have to build another tower.
And the extractinator... it gives you no where near a good amount of ores, some money, and a pet that's completely useless unless you just happen to like it.
Silt.
Wtf.