Heart of the Swarm Campaign- Kerrigan Abilities: Fury (Level 50)

This ability will be familiar to anyone who plays Diablo games and likes fast-attack barbarians- Fury causes Kerrigan’s attacks to increase her own attack rate, a boost of 15% every time she attacks that stacks up to five times, maximizing at 75% and nearly doubling her attack speed.  This ability, while not as interesting as Infest Broodlings, is a massively powerful passive improvement to your hero unit that is relevant to pretty much all situations.  Increasing her attack rate based on combat means that Kerrigan becomes a much more destructive force even without the use of her energy to power abilities, and combines well with either a Leaping Strike/Psionic Shift charge into melee range for rapid close-combat attacks or with a ranged setup that doesn’t have to worry about closing to short range with each enemy target individually.

Perhaps most obviously, this combines very well with Chain Reaction when you need Kerrigan to take out large forces of light enemies (particularly common when dealing with the Primal Zerg).  It can also be stacked with Wild Mutation for a brief burst of truly ludicrous attack speed for a large/heavy unit of Kerrigan’s nature that will rip through virtually any enemy force.  Unfortunately, this tends to compare poorly with Kerrigan’s other options for her seventh-tier ability.  Its only true advantage over Ability Efficiency is that it doesn’t require you to be using active abilities (and in fact discourages it by only boosting Kerrigan’s regular attack), and while it would be amazing to combine it with Infest Broodlings, it doesn’t go as far to enhancing Kerrigan’s use in a force or ability to keep herself in a fight.  While it’s nice to get extra damage from the Queen of Blades, the fact is that you rarely need her for her ordinary attack- enhancing it can become useful if that’s all you focus on, but her other active abilities, despite their energy costs and usual cooldown periods, are a much bigger factor in how she functions as a part of your forces in any given mission.

In the end, this is the least likely of her seventh-tier abilities to be selected not because it’s bad, but because there isn’t really much in the way of her other abilities that it stacks well with.  You’re operating as a strategist, and empowering Kerrigan to operate independently of your other units doesn’t actually help much considering that virtually everything you want to accomplish will be best achieved by rolling in a unified force to destroy your targets.