I did briefly consider the computational cost, but all the units are iterated through at the start of turn for healing and buff removal (e.g. Haste and Searing Light) anyway, so it seemed likely insignificant. Now that I think of it, having the promotion on all units is a better implementation since a unit may get the promotion at start of turn and then move out of borders. There's another corner case though - if the city with Nox Noctis is taken, gifted, or razed, all units of the old owner would have to lose the promotion immediately.
Civilization IV: 21 (Bismarck of Mali), 29 (Mao Zedong of Babylon), 38 (Isabella of China), 45 (Victoria of Sumeria), PB12 (Darius of Sumeria), 56 (Hammurabi of Sumeria), PB16 (Bismarck of Mali), 78 (Augustus of Byzantium), PB56 (Willem of China)
Hearthstone: ArenaDrafts Profile No longer playing Hearthstone.
Hearthstone: ArenaDrafts Profile No longer playing Hearthstone.
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