ULTIMA4: 2nd combat instance applies Quickness to all party members
|Ultima IV quickness combat second
|Ultima IV: Quest of the Avatar
This is a bit of a niche bug to trigger. Essentially, you need to have two enemies that are in position to attack your party serially back-to-back. The easiest way to trigger this bug is to approach the Shrine of Humility without using the Horn, as this triggers an infinite stream of Demon attacks.
The first combat instance is bug-free, but the second combat instance will apply Quickness to all party members. This means that my party members can move anywhere on the screen, and then attack--every turn. It's a beneficial bug to encounter, but it's still a bug and should probably be fixed in a future version.