I don't like the idea of 'zerg' tactics and also: my group doesn't have the jobs to do it. So in case other people want to try this with a setup that has less burst damage capabilities here's what we did:
-gave tank (pld/nin) a bunch of magic damage reduction and magic defense bonus gear which she wore fulll time. Thundaga3 does a crapton of damage.
-brought three people with erase for Cackle. Each of those also had cursna for Necropurge/Necrobane
-Tank in tunnel and ranged it (I ran in for a TA in between its spells) to give it more tp then pulled weapons into starting area to kill.
-Didn't do anything special against Thundris Shriek and intimidation. Had a rng which made a big difference in the last part of the fight. Thf shooting bolts works well with some r.acc and sushi.
In general WHM sub and Ranged Attacks help a lot in this fight. I'd go so far as saying that those two things are the designed/intended 'weakneses' of KG. Also a SAM to 2hr near the end works well. (ranged attacks and WS's can not be intimidated). Also, BRD using finale for Blaze Spikes not only saves the healer's MP, it also makes him very very likely to reapply the spikes instead of nuking you. Once weapons are down I recommend having all melee and mages stand on the opposite side of KG as the tank. The aga3's are very fast but not so fast that having melee and tank run in opposite directions won't save you. KG is highly resistant to all debuffs which also means Dispel and Stun (Finale seemed to work fine though). That's all the tips I can think of right now for all the people going the "slow and steady" road.
EDIT: This is a bit of nonsense, but I thought it was funny how traditionally in FF games ranged attacks own all flying monsters and that King Goldemar is also a 'flying' monster.
XI Wiki

