To try and stimulate some discussion of trinity comp strategies, here are my notes from my initial Mythic +0 run of Waycrest manor. I use a blood dk/resto druid/BM Hunterx3 composition.
Probably the easiest dungeon to multibox with a wide variety of compositions. No trash problems anywhere, though the devouring maggots before Raal are annoying and need focusing down and interrupting.
Heartsbane Triad: Easy. One of the only bosses where being a multiboxer might help rather than hinder, as everybody always attacks the correct target. When mind controlled, BM hunters tend to use aspect of the turtle, meaning they can't be dpsed down, but don't pump out any damage themselves. Possibly want to use turtle before the pull to put it on cooldown to stop this. There's no particular reason to stack other than for heals, so you can spread out the party to deal with Unstable Rune Mark before the pull and just turret the bosses.
EDIT: Having run this encounter with my second team who were much earlier in the gearing process, I reevaluate this fight slightly. When undergeared, its a much harder fight, both because of the high healing requirements during Malady's phase and the lack of DPS to push through the phases quickly. It feels like there's a critical mass of gear that turns this fight from the easiest fight in the dungeon to the hardest. Still not an overly hard fight in terms of multiboxing. Personal damage reduction cooldowns or, even better, immunities help mitigate the huge damage from Runic mark (even when spread correctly). Its important to be mobile through the entire phase to mitigate aura of dread.
Soulbound Goliath: My strategy was to have the team on follow and run around most of the time, basically executing the fight normally otherwise. Kill the soul thorns as a priority, though they don't take much damage. The damage to the group when you trigger wildfire is quite high, and you have to run away from the boss at the same time to avoid the Burning Souls.This makes the Resto Druid incredibly valuable on this fight: healers that have to stand to group heal will have to use a different strategy.
Raal: Straightforward. Tank stands in melee with the boss,the rest of the team stacks somewhere in the middle of the room and side steps as one when Rotten Expulsion is cast. Use follow all when he begins Tenderize and weave between the casts: the damage is not immediately lethal, so the phase is forgiving of a couple of mistakes. The fight gives you a generous amount of time to deal with Call Servant, and stuns and roots can extend this.
Lord and Lady Waycrest: Fight revolves around managing Virulent Pathogen. I start having the team follow the tank and hover roughly in the middle of the fight area. This position is chosen so that when Virulent Pathogen triggers, the team can spread without having problems with LoS or running into edges and not having space. After the pathogen triggers, I hit follow the tank again quickly as Discordant Cadenza follows swiftly after: the tank charges around to pull the team out of the swirlies then the fight repeats. When Lady Waycrest joins the fight, I focus down Lord Waycrest so that I don't have to deal with the pathogen anymore, then the fight is basically over.
Gorak Tul: Incredibly straightforward end boss. With no particular reason that everybody can't stack if you interrupt correctly, I park the ranged stack somewhere and have the tank move freely. The tank grabs the potion vials, the team focusses down the adds and burn them. Make sure interrupt the bosses casts. A very easy to execute and very controlled fight. Dread Essence does not hit hard: not sure it'll even be a problem on high keys.
