Locked in the dragon's dungeon

Made for the Monthly Jam #4 (But in two days because I joined late and then had my time cut short), with the theme of 'Locked'. You wake up in a dungeon next to a locked door. Fight your way through slimes and bats, collect gold, and find a key to get the next level of the dungeon. But be careful, if your HP reaches 0, you get brought back to the start of the dungeon. After each level you can sele…