Elysian Drop Troops
Elysian drop troops use tactics along the lines of using rapid deployment to throw troops straight into enemy lines. They are famed in battles such as the Taros campaign, the Anphelion project and defence of Betalys. They come from Elysia, a planet about 30 light years away from Armageddon. Elysians are well trained in ship-to-ship boarding actions, ambush and guerrilla warfare as well as fighting in concert with orbital support when attacking enemies. Hilariously enough, in pretty much all canon conflicts they take part in they get dicked over for one reason or another, though it's always due to incompetent command, betrayal of some allies or the fuck-ups of other regiments. Maybe they're getting slapped with some kind of bad luck, or there's some heresy going on at Forge World.
Training Elysians usually include throwing kids from the back of moving Valkyries until they learn to use grav chutes, or being shown how to clusterfuck even Orks from behind with only a lasgun. It is a good time to mention that the Guardsmen being trained to do these kinds of things all volunteered to do this, which adds some rather wiry hairs to their massive steel balls. They also often employ Drop Sentinels and the Tauros and Venator vehicles because the Leman Russ Battle Tank is too ponderous for their way of deployment.
In 6th Edition, with the ability to spam flyers from hell to breakfast, Elysians turned from "interesting tactically-flexible army" to "cheesy cheese of cheesiness," broken far beyond (almost) anything you faced before. Although, like with the Grey Knights, you can create a balanced and interesting army with lots of deep striking guardsman, multi-melta sentinels, and heavy (but not cheesy-heavy) flyer support if you do not want to be a power-gaming douchelord. And by "can" we actually mean "must", unless you want to be beaten to death with old metal dreadnought models by everyone playing with you and/or watching you play.
We have a tactica for these guys, it's here.