Follow you back to the party

Of course, Sigel Knights have the conventional tank skills: hate, and... Oh wait, that's pretty much the only conventional tank skill (unless you consider a ton of HP to be a skill, too). Well, hate is all about controlling the mob and making it hit what you want it to hit (the tank). Usually that means you run up to a mob, hit it with an agro skill, and then fight it there or let it follow you back to the party. In GD, the mob comes to you. When the Sigel Knight pulls, they are literally pulling the mob (or mobs!) towards them with an animation of chains that shoot out from the Knight's hand! Even if there's a Yul Archer shooting massive damage at that mob you're pulling, you'll keep the agro because of the Sigel Knight's exceptional hate-generating abilities.