If you mess around with the weapons a little, you may be able to get the Ice, Spazer, and Plasma beam on at the same time. Turn on the high jump boots and quickly press left and A. You should have wave, charge, and plasma already off; ice and spazer should be on. If done right, they will all be on at the same time. If you fire it, the game will either slow or freeze. Supposedly, it freezes every time unless you're in a vertically-scrolling-only area.
Go to the Equipment screen. Then highlight the Misc. item at the bottom, the Speed Booster. Then, press LEFT and CONFIRM at the right time to equip the "Spazma" beam. If you did it right, Plasma Beam becomes equipped, Spazer is still equipped, and you notice that the game glitches a bit next to Plasma, displaying some of the Varia icon next to it. If you pressed the button too early, Space Jump is turned off. If you did it too late, Plasma is turned on and Spazer is turned off.