Use shots wisely : Jump shots and crouch shots allow you to attack while avoiding enemy attacks. Do not hesitate. Keep those shots going!
Kill before being killed : if you see an enemy, shoot right away. Defeat them before they fire at you. Be the first one to attack!
Tip for taking down the fortress : Fortresses situated at the end of each level have a weak point (sensor). Concentrate your attack on the weak point!
But Destroy the cannons first. Cannons will remain even if you take out the sensor first and the fortress morphs.
Tip for 3-D levels : Destroy the weak points of each floor and stop the high voltage electric currents. Taking out the weak points quickly is key to conquering the 3-D levels.
If you press UP on the control pad and touch the electricity, you will be stunned and won't be able to move for a while. Don't move forward until you take out the weak point and stop the electricity.
After you take out the weak point, look at the map while proceeding. You'll know whether to go left or right.
You can dodge enemy bullets by lying down! Destroy rolling mines by using crouch shots.
As you proceed, there are weak points that are positioned so that you can't reach them. Utilize jump shots and crouch shots.
Beware of Falling off at Stage 4 : In Stage 4 where you climb up a waterfall, missing a platform and falling down will count as a miss.
Barrier : At specific spots in Stages 4 & 9, you can pick up barriers that make you invincible for a while. However, there is a rule : 'A barrier will appear only when you are NOT equipped with a special weapon'.