Guardian of the First Ones
THREAT NEUTRALIZATION - yellow arrows/big yellow circles - spread
DISINTEGRATION - wide white beam - avoid
FORM SENTRY (glowing orb rotating around boss) - try to avoid standing underneath
SUNDER on tank - yellow smoky circle - no-one else in that, then tank swap.
PURGING PROTOCOL - allow him to cast it once to remove sentries, then take him to an Energy Core (stone obelisk). Say within the circle around the Core.
MELTDOWN - when Energy Core melts down (large yellow swirly) move away.
There are only three Cores, so need to kill him before he starts Purging Protocol for 4th time, because that will cause constant raid wide damage.