This is a quick simple guide

The "Supreme Helper Minion" is an achievement that requiers you to complete 200 quests from the Angler NPC. You might think it isn't a lot, but then you realise those are fishing quests and in my ~300 hours of Terraria I managed to get 80 without much trying. Because I wanted to complete all achievements and this one was my last I completed it in ~1 hour using the method I will show you in this guide.

The method uses a Journey Mode character and a Journey Mode world, if you don't want to use Journey Mode this guide isn't for you.

• A Journey Mode character
  
• A Journey Mode world with Angler housed
  
• All quest fish researched*

*I recommend a Journey Mode world with all items in it to get the fish instantly
https://www.youtube.com/watch?v=bPZzpfRmH-0

The method is pretty simple:

1. Go into the Time Menu and set the time to 24×
   
2. Go talk to Angler to get the quest
   
3. Duplicate the fish that Angler requested
   
4. Complete the quest
   
5. Set the time to midnight
   
6. Wait for it to be 4:30 AM (Angler refreshes his quest every morning)
   
7. Repeat from step 2.

As you can see the process is quite simple and it shouldn't be much of a problem, if you use the world listed above where everything you need is already there it won't be as hard anymore.

One quest takes around 20 seconds to complete.

Good luck in your Terraria adventure!