The difference of offline play in Heroes II and Heroes III.

The only difference between the Amulet of Agility (UA) and other artifacts in the second game is that it cannot be captured by the enemy. When a hero with the UA is defeated, the UA mysteriously disappears...

Before versions PoL 2.1 and SW 1.3, artifacts that granted mixed skills (+6, +6), (+4 to all) did not disappear but were passed on as regular artifacts after the hero was killed. +12 artifacts always disappeared.