Bastion holds just one boss fewer than Blackwing Descent did and is widely regarded as the shorter and easier of the two instances.
The first trouble you’re likely to have in the instance is the first set of trash pulls that patrol back and forth down the hallway. The safest way to go about it is to grab one of the groups that moves closest to the entrance and then to pull the aoe packs on the left and right side one by one before moving back to the patrolling groups.
The happy first boss in this place is Halfus Wyrmbreaker.
Halfus has a bunch of dragons around him that may or may not join in the fight depending on what week of the rotation that you’re in. Each of the possible adds will grant Halfus a specific buff while inactive and assist your raid in some way if you release them.
While it’s completely up to your raid as to which ones to release and which to leave inactive, the big ones that you should watch out for includes the Slate Dragon which will let Halfus stack a Mortal Strike type debuff on the tank which will facilitate a tank switch periodically as the stack gets high.
Another is the Nether Scion which will grant Halfus a 100% increased attack speed bonus and will help alleviate that if you release him with a debuff on the boss.
The Stormrider will grant Halfus a nova type attack that does a knockback and MUST be interrupted. He makes this easier if you release him by tacking on a bit of extra cast time to that spell to make it a bit easier for you to interrupt as it comes.
The Time Warden lets Halfus’s dragon breathe fireballs and releasing him will make those fireballs take longer to land while the batch of whelps will let his dragon breathe a fiery cone but also reduce the damage dealt by said dragon.
It’s hard to lay a hard and fast strategy for this fight as it changes drastically from week to week and from what sort of group composition you managed to put together.
The important things to keep in mind and take away from this are the abilities that the various adds have and how they work together for and against your raid group. This isn’t the type of fight that you’ll manage by blindly following the same strategies for different add combinations and different raid compositions from week to week. It’s only by really taking the time to figure out what’s going to work and what’s not going to work for the various adds that you’ll manage to get through the fight with a minimum amount of fuss and muss from one week to another.