Subtle Spells for Iron-Age Warriors

[Yorunkun]

A while back, I asked for advice on building Iron Age Warriors. The playtest combat scenarios have gone well, so I'm now tackling the wider campaign. One point that's come up is the addition of "subtle magic".

The campaign will be about a tribe of Saxon mercenaries landing in Britian shortly after the departure of the legions. All the PCs will be warriors first and foremost. However, we'd like to add some setting-appropriate, low-key magic to spice things up a little - and to improve characters' chances of survival and their rate of healing. This could range from quasi-magical knacks to actual spells or divinely granted powers.

The thematic areas we're looking at including are divination, blessing/cursing, healing/necromancy and some charm/mind-affecting powers. The idea is to exclude everything that has obvious, visible effects - i.e. instant healing, or fireballs. Magic should work in such a way that sceptics witnessing its effects could always ascribe them to psychological effects, superior knowledge or blind luck. Mechanically though, magic should actually exist, and work.

My question then: How would you model these kinds of effects? I own all the relevant books (Magic, Thaumatology, Powers, Divine Favour) but have no experience using them. All suggestions welcome.