Awesome, thanks so much, Putnam, looks like I can get started on that magic system. This newfangled interaction thing looks pretty open-ended!
For good-aligned region-based interactions, there could be effects for temporary stat gain, supernatural attributes, flight, super speed and the like. For evil effects there can be strange excretions, alcohol allergies, madness, mutations, and hair loss, etc. The examples provided allow for some real horrible fates. Curses could forever turn a dwarf into a rat. Or floating guts. Or set them careening through time so fast that everybody else looks frozen. Reanimation is bad enough, but imagine the curse that paralyzes a dwarf, erases his need for food and drink, and surrounds him in a slade shell where he remains until the world ends?
Selective application/removal of tags could be horrible too. A creature that can inflict the [MISCHIEVOUS] tag could fill otherwise-normal dwarves with an irresistible urge to pull the levers they know will cause their own doom. Gas could give everyone in this town [NO_EMOTION] and you would have no idea until you woke up there feeling funny. What happens if a civ member gets hit with [VERMIN_GROUNDER]? What if a vampire makes your mayor a [PET] and unable to work - will you butcher him to free up his office? The bite of a strange Bat could make it so you never wake up from sleep. Imagine suddenly losing [CAN_SPEAK] or [INTELLIGENT]. Or the dwarf inflicted with [IMMOLATE] who must live in isolation by the lake, never to go near a barrel of booze again lest he hurt himself and everyone nearby.
There could be magical versions of ordinary creatures, like a regular animal except that it can talk and use special powers. They'd be rare and limited to Good/Evil regions and could be helpful or malevolent. You might run into a friendly taking Magical Salmon that casts a spell and gives you [AMPHIBIOUS] to save you from drowning! Or you might encounter the Accursed Porpoise that takes away your Swimming skill and paralyzes you in the water.
Adventure mode should be such that an intrepid enough explorer could learn the ancient secrets of Agriculture from a talking blue elephant in the woods that turns you into a plump helmet man if you try to injure it. Or, if in hostility you survive the encounter, you could skin the elephant and make gloves out of the magical hide that convey a bonus to Planting upon any creature they touch, and hope that the plump helmet spell wears off. Boots of levitation might be made from the skin of a magical platypus that can fly. A ring made of the bone of a certain Dragon might make any who wear it resist all illness.
It doesn't look like summoning will be possible, although controlled transformation might be useful. Some kind of ritual to become a Lich looks pretty feasible now. A [SPHERE:FIRE] deity may pass on the secrets of fireballs, conflagrations and heat resistance. A water deity could give the aforementioned water breathing tricks or the ability to morph into a blob of water. The Secrets of Literature would give you godlike Writing skills.
I'd appreciate suggestions too. These are pretty loose ideas and there are so many possibilities here, the mind boggles. Toady One is a genius.