Since Beta 10.2, Sans has Dodge (2), which lets him avoid taking any amount of damage 2 times each turn. It only counts if he actually would take damage, so 0 ATK monsters won't trigger it. This number will reset at the start of the owner's turn.
He also has the ability to give Gaster Blasters, just like Gaster himself. But unlike Gaster, who adds them to your deck at the end of each turn, Sans adds them to your hand at the start of your turn, but also when you summon it from your hand.
The Gaster Blasters themselves cost 7G to use to deal 8 damage to any monster of your choice, or 5 damage to a player. If Gaster is on the board, the player will also take 8 damage.
This can be increased even futher by using Science for your artifact.
Sans works very well in a Determination or Integrity decks since you can use Will to Fight to boost Sans' stats in early game or Another Chance to keep him alive. In Integrity, Inflation will boost him, and the soul's ability can make you able to use more blasters. Using Nice Cream Guy and Bravery spells and/or Gaster is also recommended.
Basically, boost sans' stats to make him a good card.
Countering Sans is fairly easy. You can simply Silence Sans with Scarf Mouse or Nacarat Jester, use cards that do X times 1 damage, such as Undyne or Undyne's Spears or place a card that will instantly kill Sans, such as Muffet's Pet (if wasn´t ATK boosted) Hyper Goner or Headshot. As you can see, Sans is best countered with the Justice SOUL.
- Just like any other card, a Shiny Sans gives Shiny Blasters.
- Sans's cost drop to 7G in Beta 10.2 wasn't listed in the Patch Notes.