This Seeking Tech guide will explain how you can beat Mecha Leon without taking any damage. Use the following video as a reference:
For the first step, avoid the falling fruits. When the three lizards fall down, use your slowdown power-up and then quickly defeat them.
When he starts shooting fireballs, run near the back of the arena to give yourself a few extra seconds to prepare. You can then use your power-up to slow down the fireballs to dodge this attack. Make sure you deactivate your power-up anytime you aren’t using it to keep the cool down short.
Afterwards, avoid the purple circle to dodge his tongue strike. Once you see his tongue hit the ground, use your power-up and then attack his tonsil to end the first phase.
When he shoots discs, wait until one gets close to you. You can then use your power-up to jump to the next section.
When you land, quickly make your way to the upper left corner. Wait until the missiles get close to you before using your power-up to run away.
You then need to dodge the falling fruits, before having to deal with the five falling enemies. Use your power-up to slow down time when the enemies appear. Try to defeat them as soon as possible before heading to the upper right corner.
From there, wait until the missiles get close to you again before activating your power-up and then running away.
Afterwards, you need to dodge more fireballs. The gaps are a lot smaller, so make sure you get a good angle before trying to pass through.
You then need to dodge his tongue, slow down time and then attack his tonsil.
For the final phase, you need to let the discs get close to you before using your power-up in order to jump to the pillar on the left. You then need to do the same to get to the next section.
Once you do, stay on the left side of the area. Wait until the missiles get close before stopping time and then running to the right.
You then need to dodge more fireballs. Try to stay in the back to give yourself some extra seconds.
Next, you need to avoid the falling fruits. Once the three enemies fall down, defeat them quickly and then stay away from the right side of the area.
You should then run backwards to avoid his tongue attack. Afterwards, use your power-up so that you can attack his tonsil for the final time.
Finally, pull his nose ring back to end the fight.