A mighty crystal that holds the lightning within. It is made in the most ruthless storms and used to power everything in the lands of Fjordruun. 
Volatile and rare, acquiring and stabilizing this gem is no easy task. 
Read about it at elvenfirefly.com

Properties of 1/2 lbs of crystal
AC: 23
Hit Points: 5 (2d4)
Damage threshold: 5
Damage immunities: poison and psychic
Value: 5,000 gp per 1/2 lbs, almost twice as much at the blue market.
Largest known specimen: 431 lbs, powering Mechtorn’s arc engine, capital of Automatons.

If the crystal is hit, but not damaged, or if the attack misses by 5, count as if the crystal is grazed and roll on the Energetic Fluctuation Table.
The same thing happens if it is vigorously shaken or moved around without stabilizing runes. Once rolled from the table, stormphax becomes dormant for 1 minute.
If the crystal is reduced to 0 hp, it releases stored energy, dealing 6d6 force and 6d6 lightning damage in a 20-foot-radius sphere. The crystal destroys itself in the process.

Energetic Fluctuation Table (roll d20):
Count all effects from the crystal as a central point

1. All creatures in 10' radius suffer 3d6 lightning damage.
2. All creatures in 30' radius suffer the effects of Blindness/Deafness for 1 minute.
3. Two random creatures in 60' radius swap positions.
4. A random creature in 30' radius suffers the effect of Slow or Haste spell for 1 minute (50-50 chance).
5. A random creature in 30' radius is polymorphed into a  Mammoth for 1 hour.
6. Gravity reverses in a 20' cube for 1 minute. 
7. All creatures within 30' gain telepathy with each other for 10 minutes. 
8. Objects and creatures within 30' that weigh less than 100 lbs are pulled towards the crystal.
9. A random creature in 30' radius becomes crystallized for 1 minute ( petrified ).
10. Fragile objects within 30' shatter.
11. A tiny, angry storm cloud appears above the crystal and guards it for 1 minute. It zapps anyone who reaches for the crystal within 10' for 2d6 lightning damage (max two times per round).
12. All creatures in 20' radius become trapped in a giant ice ball.
13. A portal appears and remains open for 1 minute (destination is at DM's discretion).
14. An Unseen Servant appears and will do anything to hinder crystal's disturber.
15. Up to 8 creatures within 10' radius Teleport to a random location (DM's discretion). Crystal included. 
16. All metallic non-magical objects within 15' radius transform into gold for 24h, then revert back. 
17. The closest creature is transported to Astral Plane for 1 minute. 
18. Lightning strikes from stormphax at a random creature within 60'. In an instant, it dies and then comes back to life as if Reincarnate was cast on it.
19. A series of lightning bolts strike all creatures within 20' twice. The first time they deal 3d6 lightning damage, the second time they heal for 3d6. Roll both times.
20. Stormphax self-destructs. Use the 0 hp rule.