A decent strategy against gamma king for two players. Bring the ice and forest titans (gamma should be enough), and two meks (preferably over lv 280) both equipped with high-quality M.R.L.M. modules (preferably journeyman or better, and take at least 50 pieces of ammo). Whistle attack my target to both titans, and each player mounts a mek. When the king titan has been rendered, get the titans to confront it and drive the meks around (keep hunting for the back), shoot it with the rocket pod or the pistol (be aware of the meteor shower). The gamma king would be taken down in less than 20 minutes under this stratey.

I did the Alpha king titan fight and here's what I did in both ASE and ASA, In ASE all I did was tame the titans and tame/breed 500, lvl 150 Giga's, that did the job within under an hour, in ASE which was more recent, I tamed a dreadnoughtus, about 50 Carcarahdontosaurs, 4 mechs (for the Mega Mech), and the titans and that was more difficult but still do-able but it's more difficult.

So to defeat the gamma king titan you need 4 mutated dreadnoughtuses on aggressive , an alpha tier forest titan and ice titan set on aggressive, and a mutated carcha on passive for you to ride. (Not gigas cause rage mode is possible) If the king titan starts doing an attack where it charges up its fist with corrupt energy, run away and let your titans and dreadnoughtuses handle it until the attack is done. If your stuff does enough damage while it’s charging up the attack the attack will be cancelled. If your stuff doesnt do enough damage and it does the attack while you are not far enough with your carcha, you get dismounted, you get 1 shot, and your carcha almost gets 1 shot. If you do everything correct you should be able to kill it. Stuff that is not necessary but could help: titanosaur, desert titan, carcha army, and extra dreadnoughtuses. I hope this helps.