Instructions
Sigma
Climb the walls until you are near the top. Doing this will always cause Sigma to move upwards in a zig-zag pattern.
Drop to the floor when you have a clear opening and avoid Sigma as he lands.
Shoot Sigma with the Electric Spark special weapon, which is his weakness, as he lands. It will take 16 shots to defeat Sigma or 11 shots with a charged Electric Spark.
Wolf Sigma
Avoid Wolf Sigma's three attacks by standing near the edge of the wall as he breathes fire, not standing under either claw when he shoots lightning and moving to the side as he attempts to swipe you with either claw.
Jump on the top of either claw when Sigma attempts to swipe you with it. As the claw moves back into place, you will be in a position to shoot Wolf Sigma's head, which is his weak spot.
Use the Rolling Shield special weapon, which is his weakness, to shoot Wolf Sigma in the head. It will take 16 shots with the Rolling Shield to defeat him. If you fall off the claw, wait until he attempts to swipe you again and repeat the process.