The Specimen d05 "Apex Stalker" is the strongest Stalker released, and was the Tier 7 reward of the Infected Troops Boss Strike. It comes pre-ranked when you receive it as a reward, and easily tops the amount of health exhibited by other stalkers, making it a lot less fragile.
With three different backslash attacks, the Apex Stalker has a lot of versatility. The Ice Slash and Bolt Slash attacks deal -type damage, and each have a 50% chance of Freezing, respectively Stunning, the target(s). The Fire Slash has a 75% chance of inflicting fire Damage-over-Time, which lasts longer than usual (3 turns).
The backslash attacks are very specialized, with the Flame Slash having an increased crit chance against animals, the Ice Slash having an increased crit chance against infantry, and the Bolt Slash having an increased crit chance against tanks. The regular Cleave attack at Rank 5 can deal a critical hit of up to 322 damage.