"Hey you! Yes you! Want to be 40k's Batman? Well guess what? You may just have the chance to become one without turning into an insecure, whiny torturer! Just apply for the slim chance of being recruited into the Adeptus Astartes and have an even slimmer chance of being upgraded into a Primaris Marine! But not just any Primaris Marines, but inducted into the special care of the Reiver Squad! Once you are a full fledged Reiver yourself, you can finally get the chance to swing from rooftop to rooftop with this Mechanicum approved Grapnel Launcher, all the while doing fantastic poses as the Adam West' Batman theme plays in the background. Get yours today for only 500,000,000 Imperial Credits and with a proven history of selfless valor and heroism!"
- – Imperial Advert for the Grapnel Launcher
A Grapnel Launcher is an Imperial device that uses an explosive charge to fire a grapnel hook and its accompanying filament over long distances. A Grapnel Launcher is used to scale vast heights and cross from building to building in dense urban areas. It is a piece of equipment commonly employed by the close combat stealth assault Reiver Squads of the Primaris Space Marines, who always need to be in exactly the right place at exactly the right time, ready to burst forth from their stealthy approach and attack their foe when they least expect it.
In crunch terms, a Grapnel Launcher acts more as a piece of equipment than a weapon of war which has made some in /tg/ be a bit disappointed that they couldn't yell "Get Over Here!" for shits and giggles.
When played, any models with a grapnel launchers do not count any vertical distance they move against the total they can move that turn (i.e. moving vertically is free for these models). That's of course, if they move. In addition, during deployment, you can set up this unit, if it is equipped with grapnel launchers, behind enemy lines instead of placing it on the battlefield which makes it some form of deep strike. At the end of any of your Movement phases this unit can join the battle – set it up within 6" of a battlefield edge of your choice and more than 9" away from any enemy models. Yay for the return of Outflank!