Green Dragons are the weakest of all monsters that drop Dragon Bones. Their max HP of 750 is easily overcome with Icicle Volley which deals 935 damage (748 if one of the ticks misses), or Ignite which deals 748 damage when adjusted for the Combat Triangle. These spells are therefore extremely efficient for killing these monsters. Pairing these spells with a Summoning Familiar like Witch is a good idea, as the familiar will have an chance to hit the enemy and finish it off before the players second attack.
An unavoidable attack that deals 30x20 damage over 2.85s. On a hit, has a 25% chance to inflict Burn that deals 15% of your current hitpoints as damage over 2.5s.