Much like in Undertale, people can't seem to figure out Sans' abilities.
Sans' original ability was a 90% dodge rate. This was reduced to an 80% dodge rate in Alpha 2.1, but with the added ability to put 2 Bones in the enemy's hand (which were not a spell until Alpha 2.2). These bones costed 0G and would deal 4 damage to the user.
Alpha 3.2 gave Sans the 90% change to dodge again, but would now also apply KR to any monster that gets damaged by him. Beta 2.0 decreased his cost from 8G to 6G to get more people to use him.
During Beta 3.7, he was reworked to give the player 1 Gaster Blaster and destroy 2 cards of the enemy's hand for the price of 8G, since beforehand Sans was only really used in Perseverance and Patience decks. This was then quickly nerfed in the next update, Beta 3.8, to destroying 1 card and giving 1 Gaster Blaster. Beta 4.3 changed that from instead of adding 1 Gaster Blaster to your hand, he adds 3 Gaster Blasters to you deck. Beta 5.0 increased the cost from 8G to 9G, and Beta 6.5 increased it again to 10G.
Beta 7.2 changed Sans so he gained back his dodging skills, but in a different style. Instead of a having a percentage dodging all attacks, he dodges the number of attacks listed on the card each turn, which was 3. But this was proven to be too strong for only a 5G monster, so Beta 7.3 changed that to 2 dodges. He still gives Gaster Blasters, but now he gives 1 at the start of your turn, which was how Gaster gave them before he was changed with Sans in Beta 7.2. Beta 7.6 changed that to making him give the Blasters at the end of your turn. Beta 9.1 gave Sans 3 dodges again, but also increased his cost back to the original 8G.
Beta 10.2 changed him back, not only to Dodge (2), but also made him give Gaster Blasters at the start of your turn again. However, he now also gives a Gaster Blaster with a Magic effect. His cost dropped to 7G for this, even though it's not listed on the Patch Notes. Beta 19.0 dropped his cost further to 6G.
- 8 (Pre Beta 2.0)
- 6 (Post Beta 2.0)
- 8 (Post Beta 3.7)
- 9 (Post Beta 5.0)
- 10 (Post Beta 6.5)
- 5 (Post Beta 7.2)
- 8 (Post Beta 9.1)
- 7 (Post Beta 10.2)
- 6 (Post Beta 19.0, Current)
- 90% dodge rate. (Pre Alpha 2.1)
- 80% dodge rate. Battlecry: Put 2 bones in the enemies' hand. (Post Alpha 2.1)
- 90% dodge rate. Give KR to monsters damaged by this one. (Post Alpha 3.2)
- Battlecry: Add 1 Gaster Blaster to your hand. Kill 2 cards of the enemy's hand.
- (Beta 3.7)
- Battlecry: Add 1 Gaster Blaster to your hand. Kill 1 card of the enemy's hand.
- (Post Beta 3.8)
- Battlecry: Add 3 Gaster Blasters to your deck. Kill 1 card of the enemy's hand.
- (Post Beta 4.3)
- Dodge (3). Start of turn: Add a Gaster Blaster to your hand. (Beta 7.2)
- Dodge (2). Start of turn: Add a Gaster Blaster to your hand. (Post Beta 7.3)
- Dodge (2). End of turn: Add a Gaster Blaster to your hand. (Post Beta 7.6)
- Dodge (3). End of turn: Add a Gaster Blaster to your hand. (Post Beta 9.1)
- Dodge (2). Start of turn & Magic: Add a Gaster Blaster to your hand.
- (Post Beta 10.2, Current)
Secret feature: Between Beta 3.7 and 7.1, when Sans was able to kill cards from the opponent's hand, there was a 50% change of him killing Chara if the opponent had them in their hand, no matter how many cards they were currently holding. This would change Sans's sprite and description. But, as Beta 7.2 removed the killing card ability, this easter egg was removed with it.
This same image was used for a Super colored card of Sans during April Fools' Day 2017.