On Stage 3 you can start a hidden stage theme by destroying the purple base at the bottom of the screen.
To play the first stage of Gradius and Salamander, play Gradius III until you get to the end of game final boss, he shoots three electric balls at you, don't dodge them, touch the middle ball to warp into Gradius world or touch the lower one to warp into Salamander world.
Turn Odd Number Dip Switches except Dip 1-5 AFTER boot up.
Coin A = 1 Coin/6 Credits
Coin B = 1 Coin/6 Credits
Lives = 3
Cabinet = Upright
Bonus Life = 50000
Difficulty = Hard
Demo Sounds = Off
Flip Screen = On
Upright Controls = Single
Service Mode = On
Unknown = Off
In game, hold Service Switch (Coin 3 = Key 7 in Mame) then press 1P Start Button.
Gradius IV Fukkatsu
2nd Loop Start
On the Power Meter Select screen.
Up, Up, Down, Down, Left, Right, Left, Right, Button-2 (Shot), Button-3 (Missile).
You will be able to start the game on the 2nd loop and a password will be displayed on Game Over screen. This password was required on 'Gradius IV Fukkatsu Internet Ranking' in Japan (no longer running)
Complete all the in-game missions, after the staff credits you will play the Special Stage