Race: Unaligned/None
Cost: You decide

Gain control of target building if you have 2 more friendly units/buildings units than the number of unfriendly units/buildings adjacent to it.

The building gets 6 (pick a number) control (or whatever you want to call them) counters.
Remove a counter at the end of each round.
Remove an additional control counter for each friendly unit greater than the number of unfriendly+1 units adjacent to the building at the end of the round.

Counters to be removed at end of the round:
If Friendly - (Unfriendly+1) > 1, then remove 1 + (Friendly - Unfriendly) counters at end of round. Otherwise, remove 1 counter at end of round

For every control counter, reduce the building's vision by 1 (meant to reduce the area it controls).

Use friendly and unfriendly so you don't have to go back and change it for team games.

Sounds interesting.
Best fit to Mountain Folk. Need second MF domain level.About 4 points.
Type: enchantment 4 counters.No, remove only
If Friendly - Unfriendly > 2 (same as yours), then remove (Friendly - Unfriendly - 1) counters at end of round. Otherwise, remove 0 counter at end of round or restore if (Friendly - Unfriendly) < 0. If counters become more than start value enchantment removed. Remove at least one counter each turn is bad because building can't be saved at all.Hm, not sure that it's necessary, but why not.