Got some heads up on the Spirit Crystal, that I've mentioned earlier.
For starters, it's using an action (id 50045) that has a charge time, about 2s.
It seems that it's using yet another way of controlling another character, that involves sending to client EnterDynamicRegion with mob's EntityID, some new packet (op 0x4E3A) that includes character's id and mob's id and playing around with original character + spawning extra ghost on take over.
Also, seems like I was mistaken about the golem being a pet... Was browsing through the log to find any similarities to crystal and found ChannelLogin a bit lower than I've expected, so Golem is also an NPC, that can be roleplayed