Poseidon was said to create GIANT tidal waves, storms, floods whirlpools, and pretty much anything related to the sea from nowhere. When he struck the water with his trident, a giant tidal wave would come rushing toward you. Because of this ability, he was known as the second strongest god, with Zeus in the lead. This particular power was what everyone was afraid of. Sailors were always worried that Poseidon might send out a tidal wave or storm to kill them. When Odysseus and his crew got Poseidon angry, he drowned all of the sailors with storms, sea monsters and whirlpools.
What Poseidon might do to sailors
It was said that Poseidon created earthquakes whenever he struck the ground with his trident. The angrier he was, the bigger the earthquake. Some say that he could even make volcanoes erupt! Others believed that when volcanoes erupted, it was a sign that Hephaestus was angry.
Poseidon was also known to create Islands. With a raise of his hand, a new island would appear, just like that! He could make them as big or as small as he wanted and wherever he wished. He created the island that floated around with the water so Apollo and Artemis could be born. Without him, there would be no Apollo or Artemis.
Title says all. He could summon any sea creature whenever he wanted and wherever he wanted. He could also summon sea MONSTERS!! Perseus had to defeat one of Poseidon's sea monsters in order to save Andromeda.