If attacked, the HP of the Entangling Roots should be deducted first; only after its HP is depleted would the wearer's own HP be deducted.
However, to use these Entangling Roots, one must increase the Compatibility, at least to 1% to be able to use it.
The methods to enhance Compatibility involve either using a Crystal Core or one's own HP to nourish the weapon. Using a Crystal Core would certainly consume it, while using one's own HP could leave one in an extremely weakened state…
Wang Tao suddenly thought of the Level 3 Monster he had just killed.
That monster was in a 99% weakened state and also severely low on HP. Could it have been nourishing these Entangling Roots?
If so, then everything seemed to make sense—
Wang Tao had previously doused the Entangling Roots with a lot of gasoline and then set them ablaze. The Entangling Roots were vulnerable to fire, so the flames caused them significant damage. Their HP dropped rapidly.
