Chainsaw Beam
Chainsaw Beam is the combination of Wave Beam, Spazer, and Plasma Beam while Charge Beam is unequipped. It can open doors and destroy destructible blocks that the beam is normally capable of destroying.
The Chainsaw Beam has a very high rate of fire, but has a very short range (hence the name), and doesn't have any visible effect or projectile. Damage from the beam is only dealt during a Power Bomb explosion, with a maximum of seven hits per explosion. It has the same damage type as Super Missiles.
To equip Spazer and Plasma Beam at the same time, open the inventory screen, equip Spazer, and move the marker to any of the Boots items. Then, press Left, and press A immediately afterward. Plasma Beam should then become equipped alongside Spazer with "VAR" next to it.
Power Bomb explosion
While the Power Bomb explosion is happening, firing the Chainsaw Beam will
- damage enemies susceptible to Supers near Samus' arm canon
- open Blue Doors and Blue Gates that the explosion is in contact with
- prevent Orange Doors to be opened by the explosion (blocks will still break)
- mess with the Power Bomb graphics and cause lag
Without Power Bomb explosion
Just firing the Chainsaw Beam will
- open Blue Doors and Blue Gates (including opening gates from the wrong side)
- break shootable blocks
The above items consider: 1) near Samus' arm canon; 2) any firing direction with the exception of aiming up.
