Stalker

The Stalker is a robot presumably built by Oliver Thompson and commissioned by Will Harangue in which he recorded Ben's aliens' moves in a video game motion capture-type scanning.

Its first and only appearance so far was in the episode Video Games. It recorded all but two of Ben's alien's, Way Big (being too big) and Nanomech (being too small).

While the robot's AI was designed to trace and destroy Ben's car, it's not very smart, as it once accidentally attacked a minivan that looked similar to it.

It was damaged when Humungousaur used a Sumo Slammer attack, which was not recorded into the database of The Stalker, causing it to go haywire. The defeat was followed by Nanomech, who was able to go inside it and ruin the robot's circuits in which caused it to malfunction. It was crushed by Way Big and he dropped it onto Will Harangue's car, destroying it.

Trivia

 * The Stalker does not have counter measures for Nanomech, Way Big or Sumo Slammer attacks, since none of these were used when recording all of Ben's moves.
 * It seems to be a parody of the Omnidroid from The Incredibles.
 * The Stalker has automatic and manual controls.
 * The Stalker is a parody of the Spider-Slayers from Spider-man and the stalker from Resistance: Fall of Man, as they both have the same name, move in a similar way, and can fire missiles.
 * The Stalker is a boss on Ultimatrix Unleashed on level 3.