From the Super Mario Wiki
Stone Doohickeys are red statues in Wario World. They are statues that guard the boss doors. They resemble tall, thin pillars with a crest of the [black jewel]] on top. In each level, Wario needs to gather Red Diamonds to give to the Stone Doohickey. Once enough Red Diamonds are handed over, the Stone Doohickey disappears, enabling Wario to fight the boss.