This Seeking Tech guide will explain how you can beat Lady Venomara without taking any damage. Use the following video as a reference:
For the first step, dodge the eggs from the sky and then break them. Afterwards, defeat any enemies that end up getting hatched.
You then need to avoid the shadow so that you don’t get slammed. With the tail on the ground, you need to jump and then use your rocket power-up to avoid the swipe.
You then need to use your power-up to get to the highest platform. One you get there, wait until it gets lowered near the poison. You can then jump and use the rocket to avoid getting hit.
Next, you need to get out of the purple zone to avoid another attack. Afterwards, run up against the body and start mashing the square button. You should be able to hit all the blue stones.
With her head lowered, use the rocket to end the first phase.
For the second part, you need to avoid the shadow. You then need to jump and use your rocket when the tail comes slamming down so that you can avoid the swipe.
Afterwards, use the rocket to climb to the highest platform. Once the platform has been lowered near the poison, jump and then use your rocket.
When more eggs start to drop, try to break them while staying near the middle of the area. Defeat any remaining enemies while avoiding the drill on the edge.
Afterwards, avoid the purple area and then start punching the body to break all the blue stones. You can then use your rocket underneath the head.
To end the second phase, grab the tongue and then use your rocket power-up.
For the final phase, you need to run straight ahead while avoiding enemies and boulders. You can avoid these obstacles by jumping to the sides and then hovering back onto the body when it is safe to do so.
Once you get underneath her head, use the rocket to end the fight.