Guardian of Mythal is a colossal fire elemental High dragon residing in the Arbor Wilds, south of the Dales in Orlais. The spectacular beast tends to reside near the Altar of Mythal, which it is allegedly bound to protect, supposedly at the bidding of the Elven goddess, Mythal herself.
This section contains spoilers for: Dragon Age: Inquisition.
If the Inquisitor drinks from the Well of Sorrows at the Temple of Mythal, they will travel to the Altar of Mythal to commune with the goddess. The Guardian of Mythal is summoned so that it may match Corypheus' Red lyrium dragon in battle. First however the Inquisitor must prove they are worthy by defeating the great beast in battle. The Inquisitor manages to tame the Guardian and it fights alongside them during the final confrontation with Corypheus but is slain during the fight.