Dryad's Blessing

Dryad's Blessing is a buff granted through the Dryad's NPC action. Rather than attacking nearby enemies, the Dryad casts a shield of leaves while enemies are near. All players and NPCs will gain the following effects whilst within the range of the Dryad's ability; 8 extra defense, a thorns effect (20% damage reflect) and increased life regeneration (about 3 HP/s). This is accompanied by a visual effect of a trail of green sparkles while moving.

Enemies inside the circle of leaves will be instead be afflicted with the Dryad's Bane debuff, taking 2 life per second with no boss down.

Note
The life draining effect will increase if you defeat more bosses in the world, each pre-hardmode boss (except King Slime) will increase its damage by 10%, the Wall of Flesh will increase it by 40% and each Hardmode boss (except Moon Lord and event bosses) will increase it by 15%. In addition, its damage will also be increased by 50% if in expert mode (multiplied instead of add with the boss downed effect). So, if you have all bosses defeated, the damage will be increase to about 10 HP/s (or 16 HP/s in expert mode).