[Weapon MOD] Magic Staff (W.I.P.)

Renny Bingles' Last Resort:
This staff was created by an eccentric gnome by the name of Renny Bingles. After many a year traveling with various adventuring groups and honing his magical skills as an illusionist Renny discovered the importance of a good staff. It was magically crafted with one specific purpose in mind - a last resort to stay alive.
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STATISTICS:

Staff pulses blue with red quillons as a result of being imbued with magic.

Combat Abilities:
When wielders health < 25% there is a 50% chance that the last attacker will be petrified.

THAC0: +3
Damage: 1d6+3 (crushing)
Speed Factor: 2
Proficiency Type: Quarterstaff
Type: Two-handed
Requires:
5 Strength

Weight: 3
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Looking for thoughts on this. Should I give it certain amount of charges per day or is it ok the way it is?

My original goal was to make it so when the wielders health was < 10% to teleport out of the area of danger leaving behind an explosion, but as it turns out when I used the OP code [232] - (cast on condition) if your health stays at <10% then you cast the spell in an indefinite loop until healed. Anyway, I ended up with this. Thanks for feedback.