Shiva

Shiva (シヴァ, Shiva ?) is a frequently recurring summoned monster who usually takes the shape of a blue-skinned woman with clothing of the same color. Her signature attack, Diamond Dust (sometimes called Gem Dust), deals Ice-elemental damage.

Along with Ifrit and Bahamut, she is one of the very few summons to appear in every main series game from Final Fantasy III through Final Fantasy XIV (although in Final Fantasy XII she appears as an airship instead of a summon). She also appears in every main series side-story and sequel that features summons, with the only exception being Crisis Core -Final Fantasy VII-.

Final Fantasy IV
Shiva appears as Rydia's summon after she rejoins the group in the Underworld. She is also a boss in Rydia's trial in the Lunar Ruins in the Advance and Complete Collection releases. It has a casting time of 4, costs 30 MP to summon, has a power of 120, and attacks all enemies for ice-elemental damage. In the DS release, the charge time to summon her is six seconds.

Final Fantasy IV -Interlude-
Shiva returns as a Summon spell for the imposter Rydia and Rydia in the sequel of Final Fantasy IV. Its signature attack, Diamond Dust deals moderate Ice-elemental damage to all enemies at the cost of 30 MP.

Shiva is wielded by the Frostbeast, one of four Eidolon-holding bosses found within the Lower Section of the Tower of Babil B13. Once it's defeated, it leaves behind an orb of blue light. The imposter Rydia claims the light and regains the ability to summon Shiva during battle. Shiva along with the other reclaimed Eidolons are later summoned by the imposter Rydia on B6 of the tower to battle against the party.

Final Fantasy IV: The After Years
Shiva returns in Final Fantasy IV: The After Years as one of the Eidolons being controlled by the Mysterious Girl. She is first fought in Palom's chapter, then later can be faced in The Gathering. The first time is a scripted battle, but the second time the player fights Shiva until she stops attacking, and at this time the player must do the same if they want to recruit her, otherwise she will be killed. If the party stop fighting, Shiva will recognize Rydia and will be acquired as a summon. She costs 30 MP to summon.