The Gaster Blasters are weapons often used by Sans, Gaster, and Papyrus, they appear to be a skull of some sort that releases a blast of energy out of their mouths.
- Attacking and Blocking: The Gaster Blasters are mainly used to attack its enemies, by releasing the blast of energy from its mouth, it can heavily damage its targets. It can still be used as a shield to block attacks, and can even block another blast from another Gaster Blasters tho.
- Giant Gaster Blaster: There is a much bigger variant of this weapon used by Gaster when he has 50% of his power back. He is seen using this in Do or Die. This Gaster Blaster is much bigger and uses a much bigger and more powerful blast of energy.
- Gaster Blastermination: Sans has a special attack in which he summons a big wall of Gaster Blasters towards his enemy, and this attack is powerful enough to break through shields with little to no effort. This attack however, drains a lot of Sans' energy.
- The iris color of the Gaster Blasters may vary per user. For example, Gaster's Gaster Blasters have red and blue irises, Sans' has blue irises, while Papyrus' have orange irises.
- Papyrus uses his Gaster Blasters for defense only.
- Gaster Blasters are exclusive to monsters.
- It is confirmed in the game that Papyrus can use Gaster Blasters.
- When Sans was under Bete Noire's control, his Gaster Blasters got affected as well, which can be clearly seen, due to them having pink eyes and pink colored blasts coming out of them, instead of blue.