Raid

Raid is a wave of monsters that spawn from the red monster portals. They bring forth an invading horde of monsters such as skeletons and beholders.

Completely defeating the invading force within 5 minutes gives you a large experience bonus. The portal will disappear on its own after 5 minutes.

When the player reaches level 4, a countdown with a red bar will appear at the top-right corner of the screen. The first invasion happens 1 hour from the start of the game, assuming you reach level 4 quickly enough. Subsequent waves come every 50 minutes (or 5 in-game days).

 Monster portal opened  Once the countdown is over, the bar turns bright red and a red portal opens with this alert message. Clicking on it will focus the screen on the location of the portal.

If you don't plan on fighting the horde at all or don't have a shelter, teleport your dwarves to a safe place and repair any broken wall once it is over.

Tower Defense

 * If you plan on fighting and exterminating the enemy horde, make sure your shelter is ready, has the highest comfort and one bed per dwarf. Any dwarf in danger should be immediately sent to sleep and, if overwhelmed, healed with a health elixir.
 * If your combined attack power is high enough, use the portal spell and the horn spell right on the enemy portal as soon as it appears. Enemies will get slain before they even have a chance to gather and fight back. Avoid getting pushed off into a pit by a beholder as the strategy will end up working against you. The occasional gargoyle will also cause an aura of fear and break your army's focus, so keep more soldiers coming!
 * If you lack manpower and firepower for a direct assault, delay the enemy horde as much as possible with creative use of relief, traps, cages and defense towers. Don't rely on sand walls if you want to collect loot.
 * A self-defending set of three tesla towers on both sides can deal with any threat, including flying ones. It is especially effective when mounted slightly above the surface and the walking enemies have to slowly climb or jump over a lot of obstacles. Trapping or caging targets also kills them quickly.

The goblin tribe is not part of such raids but may appear independently of it if they decide to attack at the same time.

Experience
The player must defeat the entire horde within five minutes to receive the experience bonus. Hordes get bigger and spawn faster as the player level grows, but any enemy can appear at any level.

Formula = 100 x Level2

* Percentage of experience required to next level. ** Will never cause two level-ups at level 4 and 5 by itself as total experience will be at most 3,599 XP (Level 5.90) and 6,499 XP (Level 6.81) after the bonus.