[quote=@Etcetera]
<Snipped quote by DarkwolfX37>

Either a guardian angel or an angel of light.
[/quote]

Hmm... Guardian angel is tougher because they can vary a lot, but generally you want to use something that will leave very little trace of them, since a lot of times they're connected to their charge's soul and can recover using it. Fire is the simplest but things like overwhelming spiritual power can work well also. Angels of light tend to be connected to a deity of some kind, so whatever is anathema to it would work well. Alternatively, depending on the type, poisons work well. Not because they work physically, but because of the natural corruptive nature of poisons. Though make sure it's poisonous to the species most closely related to the type of angel, for example against a valkyrie, things that are poisonous to homo sapiens is preferable.