MTG Salvation

Mardu Shadowspear

Shadowspear's ability will trigger once causing one damage to each opponent.

Double strike is a keyword that modifies the combat damage step; Shadowspear's ability only triggers when it is declared as an attacker during the declare attackers step. Double strike won't affect Shadowspear's ability.

Compare to the wording of something like Necromaster Dragon which activates each time you deal combat damage (to a player).