Martin Pulido's proposal for traps in Seeds of Chaos, an extra tactical layer on top of standard melee.

The core rules: traps are invisible to the enemy but visible to you and your allies, can be triggered automatically or by hand, and must be balanced so they help a smaller army beat a bigger one without overpowering ordinary units.

Ideas on the table included an Earthbind trap that pulls all flying units down in a wide area, dwarven land mines in the spirit of the goblin ones, and an Archer Ambush that turns into real units hiding in the trees when triggered, dealing double damage from surprise and spreading panic among the enemy.