Below we aim to outline the changes to the Raid and Loot systems of Warcraft in Legion.
How this will affect SPG Raiding will be outlined in a later update.
The most important change is that on LFR/Normal/Heroic you don't have instance locks. Instead you are "locked" out of loot from individual bosses after the first kill for the week. You can still go help your friends and run the raid 100 times, but you only get a chance for loot on the first kill each week. (unless you use a bonus roll).
For Mythic it's the old system of weekly instance locks.
The second big change is the "flexible" ride size, where the content scales with the number of people inside the instance. Similar to how the world content scales with your level in Legion. You can have people joining and leaving the raid all night and the encounters and drop will scale accordingly. You no longer need to wait for the lats couple of people to login to start the 25man or exclude a couple of poor souls just because you only have 15 people online and you are limited to 10man.
We have 4 raid tiers (the gear ilvls are for Emerald Nightmare, the first raid tier in Legion):
They each have their own loot locks, meaning you can run LFR, normal, heroic and mythic in the same week and get a chance for loot from each individually.
- LFR (Gear drop: 835+ / size: 25 / Loot: Personal): As the name suggests it's like the LFG system where you are automatically paired with a number of strangers, usually up to the maximum of 25 people, unless there is severe shortage and the system decides to start the raid with less than the maximum. In WoD the raid instances for LFR where split in sections/wings of 1-4 bosses which have separate queues in order to avoid long runs not suitable for LFR. Most of the boss mechanics are missing and it's a face roll.
- Normal (Gear drop: 850+ / size:10-30) The content is little more challenging than heroic dungeons. Most of the boss mechanics are in. Common sense is more or less sufficient to beat the boss mechanics. Can be PuG'ed with a decent group without voice comms.
- Heroic (Gear drop: 865+ / size:10-30) The content is a bit more challenging than Mythic dungeons. All of the boss mechanics are in. You need an intimate knowledge of the encounter and often addon help to beat the boss mechanics. Can be PuG'ed with well geared and experienced group, voice comms recommended.
- Mythic (Gear drop: 880+ / size: 20) This is the real McCoy. There is at least one extra boss mechanic over Heroic, which is usually extremely punishing and requires absolute coordination and intimate knowledge of the encounters. As there is raid wide instance lock and extreme challenge this is not really PuGable.
- Mythic+ (Gear drop: ???* / size: 5) This is not a raid but deserved a menton. There is a new Dungeon system, which will be extremely punishing based on the applied physics chosed before the run. It is currently understood that their are up to 10 stages, of difficulty, the item level drops from these will scale and be equal to Mythic Raid gear at the Mythic+10 level.
Another system of note is the bonus loot tokens. you can get up to 3 of them each week from various sources like your Call Order Hall buying them with Order Hall Resources, Follower Missions, (OR) and/or gold. Can be stacked to a maximum of 10 (Limits could change).
The system allows you to choose to use one of them after a boss kill and get a roll for a "personal" loot either an item from the boss loot list or a consolation sum of gold (from personal experience the chance is about 10-15% for an item). The idea being to allow you better chance of obtaining a specific item from a specific boss you need.
Even if you are loot locked after the first kill of the boss in a week you can keep trying, bonus rolls can be used indefinitely on repeat raid bosses. Obviously doesn't apply to mythic due to boss lockout, but as an example, during WoD, if you really wanted your archimonde trinket, you could kill him 3 times, bonus rolling each time, with the limit only being the amount of bonus rolls you had.
Something you may want to consider, that changed from WoD and is now Legion. In WoD, the only differences between Normal and Heroic raids were the amount of health and damage, with no mechanic differences (with the exception of Blizzard removing mechanics from normal HFC later on after its release). In Legion, Heroic raids will now add extra Mechanics (e.g. Nythendra for example has an additional debuff called Infested and a tail swipe if you move behind her in Heroic. In Mythic, the Infested Debuff is enhanced further by adding a mind control mechanic.)