Frisk

Info
Frisk is the main protagonist of Undertale.

ATK: FIGHT
Deal 3 damage to the defending character.

ABL: MERCY
If Frisk is your active character and the defending character is K.O.'d, shuffle that character into your opponent's deck.

ABL: Determination
When Frisk is K.O.'d, flip 2 coins. If either of them are heads, Frisk is not K.O'd, and put Frisk and all cards attacher to Frisk into your hand.

Tips

 * Because of Frisk's MERCY ability, you may want to switch Frisk out when the defending character is low on HP for another character to do the final blow.
 * If you're having a hard time defeating Frisk, you can use Papyrus to affect them with Puzzled. This will also disable their MERCY ability, however.
 * Another way to beat Frisk is to finish them off with Lord Business, because skills aren't activated when Lord Business K.O.'s a character.