The advertisement illustrated the three Titans: Storm Lord, Frost Giant and Dragon, not Poseidon. That being said there is a Poseidon spell jewel that gives a spell usable by Ice.
This advertisement is very old and the spell has been out since the release of the game., the spell is called Storm Lord, you receive it from the level 48 spell quest for storm wizards only, but you could use a training point at level 100.
the wizard101 advertisement showing two wizards battling malistaire drake one of them summoned I believe it was Poseidon to damage malistaire
Actually that was just Storm Lord. Those animated Wizard101 trailers showed off the Rank 7 spells of the Elemental Schools, so they're already in the game.
