"The legendary ancient stallion that fathered Sleipnir, the eight-legged Horse. Svadilfari was owned by the disguised and unnamed hrimthurs who built the walls of Asgard."
Svadilfari is a legendary mount that comes in wholes, meaning that once you get it, it is available for upgrade. Svadilfari is the strongest of the legendary mounts and can be obtained only from Royal Scouts. It has a 270 base gambit attack and gains 58 gambit attack with each level you upgrade it. It gives 7810 gambit attack at level 130 without any stars.
Svadilfari is useful when you need a strong mount for a secondary gambit hero (supposing you already have a Bucephalus or a War Elephant equipped on your main gambit hero). Your gambit hero requires at least lv. 80 to equip him with this item. However, being a legendary mount, Svadilfari is not recommended to be refined with chaos gems, just because you will need those chaos gems for stronger mounts like Sleipnir or Skinfaxi.