Blizzard awards achievements to a guild based on 80% of the kill roster being a member of the guild (click here for their exact wording) . We decided to use this as a baseline and then allow for a little more wiggle room. We currently look for 7 guild members with a boss kill before awarding them credit, but we may or may not adjust this number in the future based on user feedback. For mythic, we require 11 guild members to be present at the time of the kill. Members who transferred/joined the guild after the kill do not count towards the 11 member requirement. Our goal is to make our rankings as accurate as possible and as true to being a โguildโ raid as possible.
Note: These requirements are still in place for cross-faction. You must still meet the above requirements for a kill to count as a guild kill.