New to tanking, got a little question

Hey, I've never played a tank in my 15 years of playing mmo's, but I like this game so much I just had to give it a go after 11 months.

So I'm lvl 25 ish now on my marauder and I was wondering about something. So far I never had any aggro issues but I want to know in case I get an ilvl 130 in my party that's doing a low lvl roulette, because I refuse to be that typical low lvl DF tank that can't hold aggro and doesn't speak english.

The skill "Skull Sunder", according to the tooltip it says "additional effect: increases enmity", and AFTER that it says "combo action: heavy swing" and "combo potency: 200".

Does that mean that you get the increased enmity even if you do NOT use it in a combo with heavy swing? I'm asking because I want to know in case I get a high ilvl dps in my party, that bursts the shit out of the boss, what I can do to generate the most possible aggro, in the shortest possible amount of time (not caring about my own dps untill I have enough aggro).

IF the tooltip is correct that would mean I get the "additional effect: increases enmity" every single time if I spam it without any heavy strikes, right? Is this (at lvl 25) the best possible aggro generation? Not looking at dps, just for the sake of holding aggro against high end geared dpsers.

You get the increased enmity regardless of combo or not, but you get more enmity by comboing it due to the increased potency. The most enmity you can generate in one GCD is Overpower (edit for minor clarification: a combo'd is more enmity than 1 OP at a lower TP cost, but if you have neither prepped then OP is your best choice). Make sure to have Berserk/Raging Strikes up for bosses and DPS shouldn't pull off you, even level sync'd ones. Optimally for aggro you want to do something like:

RS pre-pop -> Tomahawk/Overpower -> Brutal Swing -> HS -> Berserk -> Skull Sunder -> Internal Release -> HS -> Maim -> HS -> SS -> etc.

There's never really a situation where you'd want to use an uncombo'd SS over just using OP, just make sure you use Provoke first if someone happens to steal aggro.

As Spooky said, you get more enmity from the skill being in combo due to a higher potency. From what many have said before, and what I've experienced myself, it isn't as simple as it being just the increased damage, but a multiplier effect. For instance, IN Shield Oath as a Paladin with Gloam trinkets, I can stomp a Paladin who is in Shield Oath with equivalent HP trinkets, however, when I switch to Sword Oath in an attempt to tone down my enmity, I am still stealing agro. So, even while losing the multiplier of Shield Oath, the higher damage along with the internal multipliers on the skills themselves still effects the higher damage and creates more enmity than what should be normal of the damage increase. So what I end up having to do is tone back some of the damage if I'm up against said Paladin. Generally, I don't have this same issue with a Warrior in HP trinkets due to Warrior's higher damage over a Paladin, plus many Warriors go for STR trinkets anyways, since their survivability is only marginally effected by their HP pool, and actually increases with more damage going out due to self heals based on damage done (Inner Beast, Storm's Path) and attack power (Second Wind).

But yeah, anyways, enmity isn't JUST enmity, your damage plays a big role too. Because of this, it's a good idea for tanks (especially warriors, since they don't have as much worry when it comes to Vitality) to carry two sets of trinkets, one with VIT and one with STR as main stats. Also, it doesn't take a lot of STR to make a difference, so focusing on getting stronger VIT trinkets while using slightly outdated STR trinkets (In the case of using Ironworks VIT trinkets and carrying a back up set of Gloam STR trinkets). This will also assure that in moments where you can DPS more in a fight, you look totally competent and l33t! Lol.