Focus

From NS community wiki

Focus makes a lifeforms primary attack more powerful, but takes longer to recharge.

Focus is a sensory chamber upgrade that increases the damage of the slot 1 ability (bite, spit, spore, swipe, gore) at the expense of attack speed. Each level adds one-third of base damage to each attack, but also increases the attack delay by half.

Fully upgraded, it increases damage to twice the original, but cuts your attack speed down to one-third.

This upgrade is especially useful for ambushes and dealing quick kills, and is often taken by Skulks, Lerks, and Fades. It is not useful for taking down buildings since it lowers your overall damage per second, however, Fades and Skulks can kill a Marine with no armor in one attack with Focus, making it perfect for hit-and-runs or when their armor has been depleted.

The largest downside is it forces the player to time their attacks, so it really hurts those who spam the attack button and charge into a group hoping to get hits. However, in the hands of a pro, it's the preferred upgrade to get the kill quickly before the Marines can respond.