Elegaius is a Magic affinity legendary from the Undead Hordes faction. Elegaius was introduced as a fragment summon champion with all players able to summon provided they completed enough fragment events. Elegaius is a mid-tier legendary that can really help you progress through waves in Faction Wars with multiple champions that are the same.
Elegaius is also a strong champion for Arena with an ability to strip 2 buffs from all enemies and reduce their turn meter, you will need accuracy to enable these skills. This works great as a champion to set up your damage dealers.
Overall Elegaius is seen as mid-tier with some areas of speciality.