Reaper Bird is a decent mid game card who draws a card from your deck into your hand when placed on the board (unless if your deck is empty, then you will take fatigue damage as usual). Best used in decks that are dependent on card drawing, such as Perseverance, Bravery, and Kindness to a lesser extent.
Since Beta 19.0, if the drawn card is an Amalgamate, that monster will gain +2 HP and Candy (which restores 3 HP at the end of each turn). This makes Reaper Bird a good asset in an Amalagamte Deck.
The Reaper Bird is an amalgamate and as such has the chance to be created and summoned by Alphys and be reduced to 3G.
Beta 21.1 gave it an updated image.