An enemy's approach triggers a nasty trap you prepared just for this occasion.

Encounter  
Immediate Reaction      Melee 1

Requirement: You must have a trap-making kit on your person.

Trigger: An enemy enters a square adjacent to you.

Target: The triggering enemy

Attack: Intelligence + 2 vs. Reflex
    Level 11: Intelligence + 4 vs. Reflex
    Level 21: Intelligence + 6 vs. Reflex

Hit: 1d6 + Intelligence modifier damage.
    Level 11: 2d6 + Intelligence modifier damage.
    Level 21: 3d6 + Intelligence modifier damage.

Effect: The target grants combat advantage until the end of your next turn.

Published in Into the Unknown: The Dungeon Survival Handbook, page(s) 20.