Ok, decided to have a go and record a video to show, how owerpowered Hagrid and plants really are.
Now first, the odds for the crown, diploma and Thorns to spawn in main arena are really slim. I scanned almost a 100 games, before i got these items. I did it, because i wanted to complete the "Thousand Emperor's Arena" quest. Experience scrolls were a bonus (Lew gets them after ~10-15 new games).
At first i went for a no-loss game, but it would have taken me a long time to ressurect, so i just went for a hack-and-slash strategy.
I paused after boss fights to plan ahead, so i could do it smoothly. If you watch it, you'll see.