I wanted to make a bossfight in my hack, but just enabling the sprite set and putting Mega Goomba in does not work. What else do I need to do in order for the fight to work? Also, how do I make it so beating the boss ends the level and transports you to the next world? My hack is a remix of Super Mario Endless Earth, so if you know anything about that games code, do help!

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Bosses usually don't work in other worlds.
The Mega Goomba is an exception to this, however.
Try copying the boss arena from world 4 into whatever level your using.
You need to have the boss control sprite, the key spawn point in the right place, and a zone for mega goomba to work.
You also need to have back background set to boss room or the boss music will not play.
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Current Hack Progress
World 1 - Complete
World 2 - W2 Castle
World 3 -
World 4 -
World 5 -
World 6 -
World 7 -
World 8 -

Game's Channel:
https://www.youtube.com/channel/UCqA5CgsW-CTfD56DCa2kvYw/channels

You are probably not going to see it but the only thing you need to do is use a boss controller (sprite type 39) and set it to megagoomba. Then place sprite 21 (mega goomba) and it should be working. To finish it you need a key location aswell, spritetype 129 and you can place that where you like.

goodluck if you read this

You could export the goomba boss battle level from world 4, then import it over whatever level area you want it in.
And then you could edit the boss area, in case you want to make it look different.






Cool website