Sneak Attack by paying ({R} magic symbol) , putting
Stormfront Riders from your hand onto the battlefield.
When
Stormfront Riders enters the battlefield, its first ability triggers, returning it and any other creature you control from the battlefield to your hand.
Stormfront Riders' second ability triggers twice, creating two 1/1 Soldier creature tokens.
Activate
Phyrexian Altar by sacrificing a Soldier, adding ({R} magic symbol) .