Monster generator
You can generate an Invader, Uber Invader, or Ghost manually if there is no suitable monster within the Watchtower's search range.
You can find more information about Invaders and Uber Invaders here. You can read about Ghosts here.
Before you generate a monster in the Navigator tab of the Watchtower, make sure there are no other monsters of the same level nearby. For example, to generate a level 3 Gascon, you must first destroy all nearby level 3 Invaders.
You can also create monsters in the "Monster generator" window. To open it, select the corresponding icon on the Global Map screen.
This icon is visible only in Kingdoms where monster generation is available.
In the "Monster generator" window, you can choose which Invader, Uber Invader, or Ghost you want to generate. If there isn't a matching monster within the Watchtower's search range, you will summon your own.
After a monster has been successfully generated, a cooldown begins before you can summon another one. This means that if you generate a Ghost, you won't be able to summon an Invader or Uber Invader until the cooldown ends.
To reduce the time until you can generate your next monster, eliminate the monster that you already summoned. Be quick, though: if another Jarl slays it, you won't be able to shorten the cooldown. The cooldown also does not reset when you change Kingdoms.
A summoned monster will disappear when that type of monster reaches its expiration time in the Kingdom. You can check the monster expiration times in the "Invaders, Ghosts, and bonuses" tab of the Events window.