Gaster is one of two monsters that attacks with the help of Gaster Blasters, the other being Sans. But while Sans adds them to the owner's hand at the start of each turn plus the turn he is played, Gaster adds them to the deck at the end of each turn.
The Gaster Blaster deals 8 DMG to a monster of your choice. Like any other spell card, it can bypass Taunt. The Gaster Blaster costs 6G to use, so Integrity is a good soul type to use Gaster with. Alternatively, you can use Gaster's high health to your advantage by using Protection (in Patience) or Glad Dummy (in general) and giving it Taunt. However, it is still susceptible to easily dying via Muffet's Pet, or being weakened by having its stats swapped around with Madjick, so have a Snowdrake or other such card on standby to give it an increased attack stat.
Ever since Beta 33.0, it lost Can't attack, so if it survives, you can use a Madjick of your own if you want to attack with an (decently) high amount of DMG.
Pairs well with Sans in a Science deck.
As a side note: Just like any other card giving cards, a Shiny Gaster will give Shiny Blasters.
- Dark Darker (by Moonlightring)
- Very Interesting (by Darky)
- Glitched Gaster (by CoreSilence)