Our Game, Slimeageddon.

You defeat the leader of the slimes at the beginning as the introduction to the game, then you work your way through and defeat the rest of the slimes infesting the rest of the kingdom/whatever setting is chosen. The slimes get progressively harder (as they have survived up until now without guidance, they would have to be stronger.) There will be different areas you will progress through as you complete the game, eventually making it to the final area with much more difficult enemies. There will be various opportunities to gain new abilities/skills, which you can use to progress through the game more easily, if only a little bit. There will be various side quests, probably “fetch” quests, which you can do on the side to gain bonus rewards.

There will be post-game rewards that will make the game easier for another playthrough, like a map with a fast-travel system, and a “deck of cards” which you can use to draw a random buff/debuff every mission.

There will be different slime types which can afflict you with different status effects on attack, or can attack you in unique ways.