Terror Unit causes Terror.
Troops who are confronted by monsters or situations that cause terror must test to see whether they overcome their terror. If they fail, they are completely terrified and are reduced to gibbering wrecks. Troops only ever test for terror once in a battle. Once they've overcome their terror they are not affected again.
If a creature causes terror then it automatically causes fear as well, and all the rules described for fear apply. However, you never have to take a Terror and a Fear test from the same enemy or situation - just take a Terror test: if you pass the Terror test then you automatically pass the Fear test, too. As any unit of Troops only ever takes one Terror test in a battle, any subsequent encounters with terrifying monsters or situations will simply count as fear.
A unit must make a Terror test if charged by or wishing to charge an enemy that causes terror.
A unit must make a Terror test at the start of its turn if there is an enemy which causes terror within 6".
Tunneling https://6th.whfb.app/special-rules/tunnelling
Tunnelling Teams aren't deployed at the beginning of the game, but use the following rules:
After both sides have set up (including Scouts), place a tunnel marker anywhere on the battlefield (a coin will do). At the beginning of each Skaven turn, except for the first, roll a D6 to determine if the Tunnelling Team emerge:
First turn: N/A
Second turn: 4+ to emerge
Third turn: 3+ to emerge
Fourth turn: 2+ to emerge
Fifth turn: Emerge automatically
When the team emerges, roll a Scatter dice and an Artillery dice. If you roll a Hit on the Scatter dice, the marker stays in place; if you roll an arrow, move the marker the distance indicated by the Artillery dice in the direction shown by the arrow.
Once the final position of the marker has been established, replace the marker with one of your models and place all the other models within 2" of the first one. The team emerges at the beginning of the turn (this is the very first thing they do that turn) and can then act normally, even declare a charge!
If the marker is moved under an enemy unit, the Tunnelling Team will automatically engage it in close combat on the side that is closest to the marker (the team counts as charging). If the marker is moved under a friendly unit or impassable terrain, place the Tunnelling Team on the closest edge of the unit/obstacle. If the marker is moved off the battlefield, the team has got lost (as per result 3-4 on the Tunnelling Mishap table).
If you roll a Misfire, roll a D6 and consult the Tunnelling Mishap table.
D6: Result
1-2: Cave in! The tunnel collapses and the team is killed. The enemy gets Victory points for its destruction.
3-4: Where are we? The team has got lost and emerges slightly away from their intended target, maybe in a pigsty, the lair of a huge monster or into the courtyard of a Bretonnian castle. The team does not take any part in the battle, but the enemy does not earn any Victory points for it.
5-6: I told you to turn left! The team almost made it, but went in the wrong direction for the last few hundred yards. Your opponent can place the marker anywhere on the battlefield and deploy the Skaven models as they emerge. The models cannot move in the Movement phase of the turn they emerge (except for fleeing if they fail a Terror or Panic test), because they are too busy trying to work out where they are and blaming each other for reading the map wrong.
