Depends how far you wanna go back.
4 Years ago he spawned in a constant place up in the "chamber" top center.
His spawn mob was just 4 Reqiuems, and afterwards would spawn ~5 Khalitzburg on certain long range attacks/skills by a xx% but with a 10 second cooldown per spawning.
Between now and then he's been changed to randomly tele, random placement spawn, but reverted back to spawning in a constant place right before the switch.
~1.5 (?) Years ago Amon Ra was made to tele on rude attack.
Present since the switch (Which is frighteningly over half a year already): "iRO" standards you see now. Even his mobs are annoying, mobs don't drop anything, and isn't really worth the hassle.