Differing from the more abundant "respawning" Fairy Gems, the supply of Dark Crystals is limited. You can only collect them once per game and location, so choose wisely on how to spend them. There are 30 of them in total.
The Dark Crystals can either be found "unpackaged", giving off an orange/black glow, or more often found inside tall vases that also glow:
Netherworld Tower (5)
There are five such crystals to be found in the Netherworld Tower:
- Nordberg Sanctuary — Past the first slide, after the second water barrier, at the southern end of behind trees, near an Empire soldier whose stuck in a Gnome's Burrow.
- Nordberg Town — Very north-north-west of the map, where Overlad spawned in the prologue.
- Nordberg Town — Entering main gate (from first Tower Gate), on the left (west) behind rocks you need to blow up using another one of the those explosive carriages from the dig site (easily missed).
- Everlight Reef — On the red/blue-key island. Near the water, on the side of the island facing the mermaid beach. You need Blues to get to the vases.
- Everlight Reef — On the yellow-key island, on the side where the mermaids are, near the water across from the red/blue-key island. Need to sweep the minions there.
- Everlight Jungle — Past the showdown with the two Mother Goddess Priestesses, at the northern end of the beach.
- Everlight Facility — Once you find the green hive, open the gate five-minion stepping stone gate to the south, in the south and west.
- Everlight Facility — In the eastern arena, about to free the first panda, in the very north-east there is a gap in the wall leading to an small "rock island" (easily missed).
- Everlight Facility — In the left (west) one of the two northern panda cells.
- Everlight Temple — After beating the Spider Queen, take the lift right to the top, there is a switch up some stairs on the right, opening the "secret" room up and to the right. Enter that room with all the chests.
- Everlight Temple Outskirts — Entering this area, the first spider webs coming from the Tower gate on the wall on the right (east) side. You will need mounted Greens to get up there.
- Everlight Town — On southern beach you will need to traverse the water with Blues, to send them through a gap in the rock.
- Wastelands Main — Just north of the Tower gate, but you will need to take the long way around the gate, down the hill, and then west and then south, between the rock face.
- Wastelands Main — In the northern village, in the north-east corner behind a hut.
- Wastelands Main — In the third village inside a tent.
- Wastelands Main — Wading in the central goo pool, near the green cave, at the east side of the ring path around the central rock.
- Wastelands Main — After fighting the two gargantuans, on the winding path, fleeing from a barrage of burning arrows, in the last bend before the slide to the Wasteland Sanctuary. Sweep minions into the gap between the rocks.
- Wasteland Sanctuary — On the lower sanctuary level, after beating the Salamander King, the previously blocked off passage from the south-east arena, is now open. The vase is right on the only path out.
- Wasteland Sanctuary — On the upper sanctuary level, after having pushed aside two Mother Goddess statues, before you cross the wooden bridge and attack the centurion, take the path up the stairs on the right for the platform above (easily missed). Note: You are unable to revisit this section of the game so you will want to make sure to get it the first time around.
Empire Heartland (6)
- Empire Harbour — In the catapult fort, in the north-east part of it.
- Empire Heartland — If you actually kill the gargantuan on the pasture with the two sentinels, you will receive a Dark Crystal (easily missed).
- Empire Sewers — Before you traverse the water using the "blocked raft" (towards the Arena Dungeon Gate), note the glow emanating from the grates under your feet. You will need to move the raft to the alternate dock, then send in the Blues to swim under the grate.
- Empire Sewers — Once inside the Empire Arena Dungeon, after you got some Blues, letting you collect a few more minions from the Tower gate, return to the room with the crane mechanism, use 20 minions to open the gate to the two Eradicators, and wipe them out. There is a vase with a Dark Crystal on that ledge.
- Empire Hills — After the second hill, were the path is blocked by rocks ahead and also to the right. Let the bombers blow up the blocked path up the steps on the right as well. Then use mounted Browns (Kelda must be First Mistress) to get to the other side of the "wall", sweeping the wolves.
- Empire City — After the fourth temple, up the stairs on the left (west) of the big doors to the Imperial Palace.