I'm writing an adventure where the heroes are exploring an ancient crypt...a very very ancient crypt, one that predates the previous age--it's tens of thousands of years old. Older than the elves. Older than dragons. Older than many of the gods. When this crypt was built, the continents were still connected. I'm talking OLD MAGICK.
(It's part of a larger archaeological "Indiana Jones meets Laura Croft" plot arc in my campaign for the resident Artificer. The party consists of 5 characters, between 10th and 11th level.)
So one of the first thing the characters are going to discover about this adventure is that this Old Magick isn't exactly compatible with their own. Specifically, modern magic items will malfunction or backfire in this dungeon. The constructs that patrol this crypt, and the magical traps that were placed here by the Ancients, tend to disrupt and interfere with the magic item attunement of modern magic items.
MONSTER ABILITIES
Here are a collection of abilities that I'm considering for my group of constructs. The weaker constructs (CR 4 or 5) will probably only have Overload or Reverberate, with the rest going to the stronger constructs (CR 7 or 8). But I'll fiddle around with it.
Reverberate (Recharge 5-6)
If the construct takes damage from a magic item or weapon that requires attunement, it may use its Reaction to deal 2d10 points of psychic damage to the creature that dealt the damage, plus 1d10 for each magic item the creature has attuned. (This is intended to be mechanically similar to Hellish Rebuke, but scales with attunement slots instead of spell level.)
Overload (Action, ranged attack)
The construct fires a crackling beam of red light at a target within 30 feet. If this ranged attack hits, the target takes 5 (1d10) points of force damage for every magic item they have attuned. Targets that do not have any magic items attuned do not take damage. (This is mechanically similar to the Firebolt cantrip, but it scales with attunement slots instead of Hit Dice/Level.)
Disruption Beam (Recharge 5-6)
As an action, the construct emits a beam of purple light in a 30 foot cone. All creatures within this beam must make a Charisma saving throw for each magic item they have attuned or lose their attunement to that item.
Stun Ray (Recharge 5-6)
The construct fires a beam of blue light at a single target within 30 feet. If this ranged attack hits, the target takes 6 (1d12) points of force damage and must make a Charisma save or be Stunned until the end of their next turn.
A creature hit by this beam can use their Reaction to end their attunement to one magic item of their choice. If they do, they take no damage and are not stunned.
BOOBYTRAPS
Don't get me wrong, the same old "Dex for half damage" is a classic, but I'm looking for something a little more interesting than simple hit point attrition. Since the premise of this adventure is "incompatible magic", I've decided that these magical traps in this crypt would react strangely to the 'modern' magic items and the way that they are attuned.
Synaptic Shock Trap
An octahedron-shaped purple crystal is hidden in a corner of the room near the ceiling, covered by years of dust and cobwebs. A DC 15 Investigation check will allow a character to find the trap, and a DC 15 Arcana check will allow a character to safely disarm it.
If a living creature approaches within 5 feet, it emits a burst of purple light. All creatures within 30 feet of the crystal take 18 (4d8) points of psychic damage, or 26 (4d12) points of damage if they have one or more magic items attuned. A successful DC 15 Charisma save reduces this damage by half.
Disruption Burst Trap
An octahedron-shaped purple crystal is hidden in a corner of the room near the ceiling, covered by years of dust and cobwebs. A DC 15 Investigation check will allow a character to find the trap, and a DC 15 Arcana check will allow a character to safely disarm it.
If a living creature approaches within 5 feet, it emits a burst of purple light. All creatures within 30 feet of the crystal must make a DC 15 Charisma save or lose attunement to one magic item. If the character has more than one magic item attuned, the player may choose which item they lose attunement to. Characters who are not attuend to any magic items are unaffected.
-----------
That's all I've got so far, but I'm looking for new ideas if you've got 'em. And if you have any feedback on what I've got written here, I'd love to hear it.