If the a new card "Catapult" gets into the game it should maybe deal damage equal HP/2 (just what has been suggested)
... but NOT the "current HP", the "full HP"
... and because we do not want it to be too strong with gravity pull + catapulting it at low (e.g 5) current HP:
"Colossal Dragon, 10
7|32
When this creature enters play, 20 damage is dealt to it:
"
"Massive Dragon, 12
8|60
When this creature enters play, 30 (maybe even 40!) damage is dealt to it.
This+Catapult would make it usefull...