Does Anyone know

[Quitti]

any 'Onebattle spell' effects that only target the master will target the slaves, so for example having a Lantern shield that casts corpse candle as onebattle spell does not make all the slave equally cast the spell or gain the benefit of it (makes sense, right). Effects that only affect the 'caster' (ie. the holder of item) transfer to slaves. Copper plate is one of these, as vfb said. There are some items that I have no idea if their effects transfer, most being artifacts (like Armor of Virtue returning, which is set as onebattle spell).