Golems of the Starlight Dimension and How to Beat Them
Eternal Starlight has four golems, and only one of them is a boss. The Starlight Golem is the fight that gates golem steel and the Alloy Furnace; the Astral, 
Grimstone and Aethersent Golems are ordinary hostile constructs you will meet while exploring. Knowing which is which saves you from preparing for a boss that was never one.
The Starlight Golem
The mod's own notes describe these as machines built by the ancient Starlighters to serve the mechanical giants that defended the dimension, and add that no intact golem survives to the present day. What you fight is a reactivated one.
Two things define the fight:
- It does not move. The golem is described as an imperfect being that stays where it is, which lowers the difficulty considerably. You control the distance, so you can retreat, heal and come back without it chasing you.
- Its armour is the whole problem. Under normal conditions the armour is very difficult to penetrate and your damage barely registers. The opening comes when the golem stops attacking and begins absorbing energy. At that point it is relying on energy blocks, and extinguishing all of those blocks temporarily deactivates its armour. That window is when you do your real damage.
Fighting it by simply swinging harder does not work. Watch for the absorption phase, kill the energy blocks it is feeding from, then commit.
Where to find it
The Starlight Golem lives in the Golem Forge, an underground structure whose entry room is the boss chamber itself. Inside you will also find chests holding basic industrial supplies - stone, coal and charcoal in quantity, among other things.
A 
Starlight Golem Spawner block exists as well, which is how the encounter is started. The spawner block itself has no drops, so do not expect to carry it home.
What it drops
The boss is worth the trip:
- 8 to 10 Oxidized Golem Steel Ingot
Oxidized Alloy Furnace - the only source of the Alloy Furnace, the mod's ore-doubling and unrealium machine- A forge armour trim
Smithing Template 
Energy Sword- A
Music Disc carrying the Mechanical Fossil track 
Starlit Painting- The common boss drop pool on top of all of it
The alloy furnace is the reason to prioritise this fight. Everything downstream of it - doubled ore, cheap netherite, golem steel and unrealium - is locked behind killing the golem once.
Both the furnace and the ingots arrive oxidised. Scrape them with an axe to clean them up, and wax them with a 
Honeycomb or 
Raw Amaramber if you want them to stay that way.
The three ordinary golems
These spawn as regular mobs rather than bosses, and their value is in what they drop:
- Aethersent Golem - drops 2 to 4 Aethersent Ingot and 2 to 4 Raw Aethersent. This is the best of the three by a wide margin, because it hands over finished ingots as well as raw material. Aethersent is the metal behind the mod's arrow, armour and cape line.
- Grimstone Golem - drops 0 to 2 Grimstone and 0 to 2 Cobbled Grimstone. Building stone, essentially; it is not worth hunting for loot.
- Astral Golem - drops nothing at all. Fight it only when it is in your way.
All four use a beam attack, so ranged pressure and cover matter more than melee reach when you are dealing with a group.
Golem steel, the material
Golem steel is what the whole golem line exists to supply. The 
Golem Steel Ingot is alloyed from 3 Deepsilver Ingot and 2 Golem Steel Nugget in the Alloy Furnace over 400 ticks, and it is one of the four ingredients in 
Unrealium Ingot, alongside deepsilver, 
Malarite and 
Soul Dew.
As a building material it comes in a full set - blocks, tiles, slabs, stairs, pillars, bars, grates, jets, crates and chiseled variants - and each of those exists in plain, oxidised and waxed forms. Since the blocks weather over time, plan your build with waxing in mind: place first, decide on the finish, then wax the whole surface so it stops changing.
An order of operations
Find the Golem Forge, read the golem chapter in your 
Glimmering Tablet before engaging, and go in with a plan for the energy blocks rather than for the golem itself. Take the Oxidized Alloy Furnace home first, clean it with an axe, and set it up before you spend any more time hunting the smaller golems - with the furnace running, the aethersent and deepsilver you collect afterwards go much further.
Covers the mod's in-game guide topics: