Through the gloomy haze of dusty air, you can make out four pairs of glowing purplish points of light, side by side, located in four separate locations in the crypt. As soon as (lead party member) steps into the crypt, the rattling sound resumes, louder now, coming from several directions. A few mirror-like rock crystals glint in the light from the walls and ceiling. You can faintly make out an uneven domed ceiling, which appears to have dangling, dust-laden cobwebs in places. The sound lasts only for a second, and you now see a line of coffins/sarcophagi etc.

Even the tiniest sound echoes eerily, and the floor covered in a layer of thick dust causes a puff of hazy dust to rise into the air as the door swings open As your eyes adjust and your (torchlight/darkvision/light spell, etc.) penetrates the gloom, you heard a faint, almost imperceptible rattling sound, like dominoes scattering on a tabletop.

'As the door swings away into an inky black crypt, a sudden chill runs up your spines, and you sense something deeper even than the darkness lies within the chamber. DC 10 or 12 Wis save for characters or they suffer -1 or -2 on attack rolls, saving throws, and ability checks in the area (depending how dreadful you want to make it) new save to avoid for 24 hrs at the start of each of their turns. They could be animated by spiritual focus, which also radiates a dreadful presence in a 60' or 90' radius. Alternately, you could cause them to glow with an ethereal sickly purple light, granting them +1 to AC. For a different twist, suppose that there is a special brand of necromancy at work in this particular tomb or your whole campaign that has origins in divine lore (perhaps the necromancer at work here worships a particular deity that has granted it limited powers to imbue undead with some divine spell casting power), and select individuals of the dwarf skeletons can cast one or two cleric cantrips. Approximately three of them would be roughly equivalent to four book skeletons, so CR 1/2 rather than 1/4. They'd carry dwarf weapons like the mace, battle axe, warhammer, doing 1d8 +3 instead of 1d6 + 2 damage. I'd maybe do dwarf skeletons with 16 CON and 12 STR, that wear more complete armor (AC 14 or 15). Just be careful not to imbalance things or pose a quandry the party isn't capable of solving or surviving. It's always good to give your monsters some twists that players won't know from reading the MM. (Assuming a homebrew campaign) You are the DM.

Phandelver and Below: The Shattered Obelisk Mordenkainen Presents: Monsters of the Multiverse

Minecraft kin skeleton king