The shotguns are the best weapons to use, followed by the bazookas. Make sure to upgrade them regularly while saving to buy the Jackhammer. Handguns, machine guns, rifles, and the Squid Launcher are less effective. The weapons you have available at the start and at checkpoints are random. Make sure you only have effective weapons that are upgraded in your arsenal. By firing your weapons proactively, you can prevent damage to yourself. Repeatedly tap the center of the screen to take out opponents before they have a chance to harm you.