Vinethesis

The Poisonous Flower; Vinethesis is one of the Lost Woods Colossal Titans you'll come across in Titan Souls.

Tips for Beating
Begin by trying to attack the "tentacles" at the root to give you a bit more space to move around. Be cautious though since they can still kill you despite not being attached. They'll begin to grow back, which is tricky, but you'll need to target his mouth after he blows out the smoke, specifically when he inhales. Once you've pulled your arrow back, you'll expose his eye, enabling you to shoot it. Note that the gas cloud doesn't immediately kill you, but if you stand in it too long it will.

A quick way to kill this boss is to run to the far right side of the stage immediately after engaging him. Wait his standard three slaps and then run up close and slightly to the left of his mouth. Fire in your arrow and immediately start pulling it out. If timed correctly, you should be able to fire your arrow into his weak spot immediately after you retrieve it.

Another slightly safer way to do this fight quickly is to instead run to the left side of the arena after engaging him, baiting over the cloud. When he starts spinning the other way, run to the bottom of the stage and fire your arrow into his mouth, then quickly pull it out. Wait on the far right side of the arena, and when the boss circles around, shoot him in the eye.