Black Mesa: Definitive Edition - 16 - Gonarch's Lair [Hard]

Chapter 16: Gonarch's Lair

Having jumped through the portal at the hub, Freeman finds himself on a new island in the borderworld, with the Tower still a ways in the distance. Finding an abandoned teleporter, he re-activates it in the hopes of using the equipment to transport himself to the top of the Tower. However, before he can do so, a powerful Xen creature known as the Gonarch emerges and destroys the teleporter, stranding Gordon in her domain. With no other way to get closer to the Tower, he must travel through the Gonarch's Lair on foot in a deadly game of cat and mouse while contending with her headcrab offspring.

Playlist with all completed chapters:
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Notes:
The Baby Headcrabs that Gonarch spawns will die after a short period of time (4:13). They will remain idle if Freeman isn't close by
If Gordon stays on the healing pool island at 4:28 even after it's destroyed, Gonarch will "shell" the island with her mortar and spit attacks to force him to move
Rocket hits on the Gonarch while she's charging do not always stop her - this may be dependant on her distance to the player (5:46)
The secret portal at 8:09 can only be entered after defeating the Gonarch
The teleporter at 14:40 is linked to the one ontop of the ledge in the final arena at 36:02. It was set up by the survey teams in order to bring a gas canister to Gonarch's Lair to kill her. If Gordon had brought the canister from the research base in the last chapter to this point, he can use it to kill Gonarch as per their plan by sending it through the teleporter. During the final battle, the pathway at 35:53 will then open to allow Freeman to access the ledge and activate the gas
Alternatively, Gordon can spare Gonarch by simply teleporting the canister to open the pathway, then scaling ledges along the top of the room to leave the arena without battling her
Damaging the Gonarch enough at 15:49 will cause her to temporarily retreat to cover, but she will always come back to attack him
It is impossible to successfully traverse the webbed platform at 16:12 before it falls (to my knowledge)
Jumping onto the spiked growths at 25:32 will severely damage Gordon
If Gordon stays within the alcove on the left at 29:05, Gonarch will continue to try digging him out after her charge
The following actions were done for dramatic purposes and isn't needed to progress the battle:
Shooting the detonator at 21:23
Shooting the crystals at 37:13

Trivia:
Nihilanth's comment at 0:01 may be noting the fact that, despite Gordon's best efforts in HL1, the Combine eventually take over the Earth anyway in HL2. It can also refer to the G-man having complete control over Gordon's fate by the end of the game
It is implied that the Vortigaunts had set up and possibly used the teleporter at 0:59 in the past in order to get to the Tower. However, due to the presence of the Gonarch they may have vacated the area shortly afterwards, leaving behind their equipment
In HL1, the Gonarch is already present at the start of the chapter as Freeman portals in from the hub. In BM, she instead appears only after Gordon activates the teleporter (3:54)
Most of the white crystal clusters in the first arena can be destroyed if Gonarch runs into them (4:22)
The Gonarch’s mortar attack from HL1 returns, albeit with a green blob rather than white - see 4:46
If Gordon keeps following Gonarch as she runs away at 6:37, it can be seen that she runs into the alcove at 7:06
The secret portal/room at 8:36 contains many easter eggs and elements of the game's ARG. More notes on this room can be found in the comments section
Starting on the second map of this chapter, the dead bodies of survey teams 2 and 3 that were referenced in the previous chapter can be found. There are 7 bodies total, with the last one impaled on a spike at 38:31. Team 2 was sent to kill the Gonarch, while Team 3 was to recover Team 2 after their unsuccessful attempt
The area at 19:11 is the first glimpse of Xen Gordon saw when he was teleported during the Resonance Cascade
If Gordon keeps observing Gonarch after evading her at 22:09, it can be seen that she climbs into the alcove at 22:23. I did not show this because she will simply keep trying to swipe at Gordon if he stays at the cave opening
If Gordon shoots Gonarch at the start of the third map from the spot at 25:57, she will immediately trigger the arch to collapse instead of waiting for him to get closer
Fast headcrabs, an enemy in HL2, can be seen scaling the wall at 27:55 amongst the other Standard headcrabs. This is the only instance in the game in which they appear
Gonarch falling from the top of the webbing is a callback to the same final sequence in HL1’s battle
Dead Baby Headcrabs can be seen in the Gonarch’s eggsac at 38:21
The various chase sequences in this chapter are very reminiscent of the Antlion Guardian chases in HL2:EP2