Ok so I was thinking of putting the BotWorldDragon on a BSB who goes with an Archmage in a bunker of Phoenix Guard.
The Banner rule, which seems pretty all-encompassing, reads:
"The unit is completely immune to all spell effects, whatever their source. This includes friendly spells, bound items and spells with area of effect that were cast on nearby units, etc. Spells which are cast on another unit, such as Flaming Sword of Rhuin, will work as normal, as will all magic weapons used to attack them."
Seems to me the only reason for putting that second sentence in, is because they assume a Mage (a unit in its own right) may be part of the unit carrying the banner, and may want to cast spells on himself. It goes without saying that a Mage could still cast spells out of the unit - so the choice of FSoRhuin, which is often cast on the Mage himself, is to illustrate that self-buffs are fine.
I understand that I can't cast spells on said unit due to the Banner, but can my Archmage cast, for example, Throne of Vines on HIMSELF, as it is a spell that doesn't affect the unit, only the mage?
I can see an argument either way - once the Archmage joins the PG, he counts as part of the unit I assume.
What do you guys think?