Now that Sload Grinders has achieved that, next up is 0 portal. The buffs and debuffs I tried to keep up as much as possible were Minor Berserk, PotL, Elemental Drain, and Major Slayer.
Concerning Elemental Drain the off-tank kept it up on the minis when he was upstairs, and popped it on the main boss at the beginning of the fight, which allowed me to focus a bit more on other things.
Concerning Major Slayer- wearing Roaring Opportunist, 1 heavy attack will proc the buff on 6 groupmates, and heavy attacking a 2nd time will subsequently proc it on the last 6 who did not receive the buff the first time, which is why I heavy attack quite frequently during the fight.
In the future, one improvement I'd try to make would be to begin heavying a bit sooner when the set is near to coming off cooldown, at around ~2 seconds prior, and to better line up the procs with boss ports.
This set now scales in duration based on the caster’s Spell Damage and Max Magicka, rather than based on the damage of the Heavy Attack that procced it. The current values are 1 second per 1000 Spell Damage and 1 second per 6000 Max Magicka. The intended values are the ones listed on the tooltip, which will be fixed in a future patch.
What this means is that to determine the duration of Major Slayer you will get, you can use the following equation, based on the "current values" as noted in the patch notes: (Spell Damage / 1000) + (Max Mag / 6000) You will want the result to equal or exceed 12, which is the maximum possible duration of Slayer (without Jorvuld).
With this in mind, you can play around with your stats until you find something that gets you the numbers you need to reach the 12-second duration. When testing this on my own, I like to hit the trial dummy to see what my stats will look like in a raid-buffed scenario, though you can still get a decent-ish idea of what your Slayer duration will look like without doing so.
You don't have to copy this exact setup to get the maximum Slayer duration, which I think is really cool! Pick whatever works best for you, experiment, and/or build yourself around what your group needs.
If you're wondering why I was using Restoring Focus, it's because I was playing around with it to see the impact it would have on my stamina sustain, since sometimes it got really sketchy if I needed to dodge roll/block/break free a lot with keeping up PotL on numerous targets.