Charge Worm

The Charge Worm (Officially known as Deorem according to lore but nobody would actually know that) is the first boss you will encounter in Zero Misison. He spawns when you enter the room where you collect your first missiles, but only after you've collected the missiles. If you fail to defeat him, which can happen if you miss all your shots or run out of ammo, he will leave and return to fight you right before the first Energy Tank.

It takes 3 missiles to kill this worm and it rewards you with the Charge Beam after defeating it. Normally you will need to wait for it to open its eye and shoot it one at a time, and hoping it doesn't throw spikes at you because they waste more time to watch the spike animation. Most runners will attempt a strat called Doubles, which involves shooting a missile and immediately jumping to fire a 2nd missile so that they both overlap and hit the worm's eye on the same frame. There isn't much of a cue for this trick since it's all timing, the best advice is to practice with save states until you figure out a timing that works for you, and then continue practicing that timing to build consistency.

There are two opportunities to hit the double, either during the first round or the 2nd round. If you miss both rounds, the third missile will kill him anyways so there's no reason for a double. Attempting and failing the double both times only costs exactly 5 missiles, so there's no reason not to go for it, but it's also not worth resetting your run over missing it unless you're going for top times.

If you hit the first double, you get the opportunity to do a dboost into the worm to kill it even faster. You need to hold angle+down and position yourself near the right side of the worm after hitting the first double, and as it's lowering towards you, you run into the worm to get iframes and shoot its eye right as it opens.

Quickest Kill

Quick Kill

Regular Kill