This hack is meant to be like Boss Endurance from the kirby games.
Use your level ups strategically and beat the first 4 bosses in an order that works best for you, then use your remaining strength to defeat the last 4 bosses.
You have 1 life
Level ups cost less so you'll be somewhere around the appropriate levels for each boss
Magic and Life do not refill when you level up
You cannot save until you beat the game
You have every spell except Fairy
You can get the down thrust technique after beating 2 bosses (It's blocked by 2 locked doors)
There are 2 red jars: First one in a cave behind 1 locked door, second one just before thunder bird
Some other changes could be made for the title screen but it's fine for now.
Try it out and leave a comment
Here is the chart of level up point requirements if you want to plan it out: