The Deathstalker is a type of Eldar Super-heavy grav-tank that have never seen the days on tabletop since the ye olde age of Epic. From what we can tell the Deathstalker is armed with a heavier version of the Prism Cannon meaning that it is essentially the Fire Prism on steroids and seeing how OP the Fire Prism was on both tabletop and Dawn of War Emperah help us if Forge World decides to have an update on this beast.
We know of its weaponry due to the very obvious ECKSBOXHUEG crystal situated at the back of the cannon. While this may make the tank unable to have a turret to swivel around for efficient shots as well as having the entire vehicle to move in order to aim. It is compensated for the very obvious firepower this monstrous son of a gun can effectively wield in the heat of an intense engagement or combat.
According to age old fluff, multiple Deathstalkers can combine their fire into a chain to produce a much more powerful blast, meaning that this thing has the potential to turn your Titan legions into slag of molten metal