The Mad Flower at the End of the Road is a Genshin Impact Challenger: Series VI Achievement that can be obtained by paralyzing the Electro Regisvine when it emits a beam of thunderous light. I had so much trouble getting this Achievement—it took me months of casually trying to figure out how to trigger the attack. It's actually not that hard, but you need to set up the battle properly so that all the requirements align.
How to paralyze the Electro Regisvine by attacking its corolla when it emits a beam of thunderous light in Genshin Impact
First, you need to visit the Electro Regisvine's cave south of Mawtiyima Forest. Like most Regisvines, this will have an Electro shield alternatingly across its corolla and roots. You need to use either a Pyro or Cryo character to break the shield to paralyze the boss.
Upon starting the battle, the Electro Regisvine's shield will be at its corolla, circled in the image above. Your goal is to reduce the shield to as little as possible without breaking it. Consider using a Pyro or Cryo archer like Amber, Yoimiya, Diona, and Ganyu, as the corolla is hard to reach using melee characters.
After the shield has been reduced, wait for the shield to transfer to the roots. Don't touch the boss at this point. Wait for it to return to the corolla.
When the marker on the ground appears (circled above), get rid of it using a Pyro or Cryo sword user, such as Bennett.
Related: How to get the Resistance is Futile! Sumeru Achievement in Genshin Impact
Next, you need to stay as close as possible to the boss. Reference the image above for how close you need to be. It's impossible to trigger the "beam of thunderous light" without getting as close as demonstrated above.
This is where RNG comes into play. If you're lucky, the Electro Regisvine will trigger the beam of thunderous light. It starts by shooting lasers to the left and right, pictured above.
Finally, the Electro Regisvine will emit a beam of thunderous light, which looks like a giant laser (see above). While the boss is shooting the beam, use your Pyro character to quickly break the last bit of the Electro shield in the corolla, meriting you the Challenger: Series VI Achievement "The Mad Flower at the End of the Road."
For more Challenger: Series VI Achievements, check out How to get the I Can’t Take It Anymore! Sumeru Achievement in Genshin Impact here on Pro Game Guides.