Guerrilla Tactics

Guerrilla Tactics deals 2 damage to any target.
When a spell or ability an opponent controls causes you to discard Guerrilla Tactics, Guerrilla Tactics deals 4 damage to any target.

The List

Tenth Edition

Guerrilla Tactics deals 2 damage to target creature or player.
When a spell or ability an opponent controls causes you to discard Guerrilla Tactics, Guerrilla Tactics deals 4 damage to target creature or player.

Ninth Edition

Eighth Edition

Discarding as a cost to cast a spell will not trigger the ability. Only discarding as an effect will trigger the ability.

If it is discarded, the damage done by it is done by this card due to an ability and not by a spell.

The second ability will trigger even on an optional discard caused by an opponent.