Sky Furies are a variant of Vikings built by Arcturus Mengsk in Co-op Missions. They are powerful anti-air and anti-ground attack that does large amounts of damage to massive units. They can be upgraded to temporarily have 50% increased damage upon transforming at Rank 2, and at Rank 3 can evade attacks in the air and move into the air upon taking fatal damage when in assault mode.
Killing enemy units grants experience to nearby Royal Guards. If there are no nearby Royal Guards when an enemy is killed, the experience is instead split between all Royal Guards in the mission. Experience allows the unit to gain Rank, which improves its damage, armor, health and unlock new abilities or passive bonuses.
Rank 1: Deals bonus damage to Massive targets.
Rank 2: Gain the Tactical Realignment ability.
Rank 3: Gain the Evasive Maneuvers and Phoenix Protocol abilities.
The leveling up mechanics works as follows:
When an enemy unit is killed, 100 experience per supply cost of unit killed is "dropped".
If the unit is a non-Heroic unit with 0 supply cost, it will drop no experience.
If the unit is a Heroic unit with 0 supply cost, it will drop 800 experience.
Dropped experience is equally split among all eligible units (Royal Guard, not at max rank) within 15 range of the unit killed.
If there are no eligible units within 15 range of the unit killed, all eligible units on the map get an equal split of the dropped experience.
Once a Royal Guard unit has reached maximum rank, it is removed from the pool of eligible units so as to not waste experience.
Mastery: Increases the gained experience per supply by +0.5 (+4 on Heroic unit with 0 supply cost) per Royal Guard Experience Gain Rate mastery point. Up to a maximum 115 experience per supply (920 experience on Heroic unit with 0 supply cost).
Royal Guards increase Imperial Support based on their supply cost and Rank. Each point of Imperial Support generates 1 Imperial Mandate every 240 seconds.
Imperial Support=50% for Royal Guard's Supply. Depending on the Rank level, the number of Imperial Support increases by x2 (Rank 1), x3 (Rank 2) or x4 (Rank 3). Mastery: +1% of Imperial Support per Royal Guard Support mastery point. Up to a maximum +30%.
The Sky Fury was designed in Co-op Missions in reference to the Heart of the Swarm opening cinematic, where a Viking lands to fight an ultralisk only to be crushed. According to Co-op director Kevin Dong, the Sky Fury's bonus vs massive was designed to make it powerful vs ultralisk as a means to "redo" that part of the cinematic.