Tip: You can use Lunar Magic's Overworld Layer 3 Editing system to edit or create your own layer 3 images (castle bricks, fish, rocks) and apply unique effects per level via the Layer 3 Bypass in the main editor.
Mercenaries is a type of hack that has no exits. Now you're probably thinking, "why did this guy put no exits in his hack, or maybe, "if there are no exits then how are we supposed to beat the hack?!?!!?" All you have to do is rack up as many points as possible before the game is over. A text document about how to play the hack is included. The text document has all the rules and some very useful advice when playing Mercenaries.
This is an arcade-style hack with no exits where the objective is just to get as high of a score as you can. You can earn extra lives by keeping hit combos going enough and thus max out your score. The big, one-room levels have a lot of similarity so you can play what suits your aesthetic tastes but at the same time it's disappointing because different styles in enemy setups may favor different players' skillsets for score farming.
The biggest downside of this hack though is it does not save high score, so once you get a game over, it doesn't matter at all. If you didn't pay attention to your high score at the end of the game, it's lost. I would think a better way to implement this gimmick if you want your game to encompass it would be to do away with the file system and have high scores listed on the title screen instead and only the option to start a game or delete a high score.
...That's why I can't really rate this hack high. It doesn't accomplish what it sets out to do.