Magic item idea - Idol of Chaotic Might

The Idol of Chaotic Might stands 3' tall and depicts a human-like robed figure holding a long, ornate staff. Where its face should be, however, under its hood, writhing tentacles jut out at odd angles. The Idol is made of an indeterminate jet-black smooth stone and is meticulously crafted, almost lifelike in its figure and posture.

It radiates a powerful aura of Chaos and glows brightly in a bloody red color if Detect Magic is cast on it.

Any spellcaster casting a spell within 10' of the Idol must save vs. Spells, or instead of his intended spell, a random spell of the same level will be cast. If he succeeds, his intended spell is cast. In any case, the spell is maximized - has the maximum duration, maximum damage and so on, and any saving throws against it suffer a -2 penalty.

I like it.