The Angel of music appears as three alabaster-white cylinders hanging in mid-air, each shorter than the last. Disturbing one of these cylinders will produce a clear, resonant tone. Each cylinder a different tone. After three tones have been produced all living creatures in earshot will be affected in one of three ways:
1) Reduced in age to the time their kind is first ambulant.
2) Set to the prime age for their kind.
3) Increased in age to the time their kind is still just barely ambulant.
And then the Angel teleports to a random location nearby.
To keep things simple, I would tie the effect to the first cylinder hit. To keep things unpredictable I would determine this randomly. In other words, the smallest cylinder doesn't necessarily turn everyone into a toddler. But if I rolled that cylinder "B" is the youthening one, then any three tone sequence that starts with that cylinder will turn things into toddlers of their kind.
You have to hear the tones for the effect to work.
For the second effect I would make it a complete refresh: parasites, scars, tattoos gone, lost limbs regained etc. This could serve as the bait (they've read about it somewhere and want to get an eye back or something) that could make a cautious party mess with the Angel at all.
If this interests you see this and this.