Animated swarms

In Wednesday's D&D game, the party ran across a being -- or force of supernature -- that inverted the animate status of things. When it encountered living tissue, it made it non-living, petrifying it. Where it encountered nonliving tissue, it animated it. This meant some grisly encounters, such as animated suits of armour filled with the crunching, petrified bodies of soldiers.

Also, the area was full of swarms of small animated objects -- not just the suits of armour, swords and so on that you find in the Monster Manual but also knives, lamps, bottles and what have you. I decided I would treat these like the swarms of small creatures you get in the animals section of the MM.

Relevant image stolen from here.

I wanted this enemy to be a dangerous nuisance with some fun special effects rather than a huge damage-doer, but I didn't mind making them reasonably beefy given how tough my PCs are.

In fact, the PCs ran like the wind as soon as they encountered one of these swarms, having knocked it out with dispel magic.

Swarm of animated items
Medium swarm of Tiny constructs, unaligned
AC 14 (natural armour)
HP 26
Speed 5 ft., fly 30 ft.

Str 12 (+1), Dex 15 (+2), Con 11 (+0), Int 1 (-5), Wis 5 (-3), Cha 1 (-5)

Saves: Dex +4

Damage immunities: poison, psychic. Condition immunities: blinded, charmed, deafened, frightened, paralysed, petrified, poisoned
Damage resistences: bludgeoning, piercing and slashing

Antimagic susceptibility, deceptive appearance, swarm

Senses: Blindsight 60 ft, passive perception 7

Type (if no type then just household junk):

1. Knives. Attack +5, 4d6+4 slashing damage, 2d6+2 if on half HP.
2. Lamps. Attack +5,  4d6/2d6 fire damage, Dex save DC 14 or light one flammable object. Vulnerable to fire damage. If hit with area fire damage, explodes, causing 6d6 fire damage in all adjacent spaces (Dex DC 14 halves). 
3. Pots and pans. Attack +5, 4d6/2d6 bludgeoning damage. AC 15. 
4. Chemical vials. Attack +5, d6d6 damage. 1-3: acid, 4-6: poison. 

Now, how to do these as a frugal monster.