Loren was added in Beta 8.2. Previous Versions can be found here
While Loren is in play, the opponent will take 1 damage for every monster that dies, including your own.
This can be very useful in combination with Mettaton NEO or Hyper Goner, as it can lead up to 5+ damage alongside the board clearing.
It can also be useful alongside Asgore, which makes this do a max of 4 damage, but without the need of sacrifcing any of your monsters.
And a third useful way is combining it with Papyrus or Undyne against cards like Rock and Lamp, as Rock and Pebble count as 2 different monsters, leading to 2 damage to the enemy.