I find the trick to designing cool battles is to think of challenges you can present to the player, then design tools for them to overcome those challenges. My favorite fight system doesn't actually come from RPG Maker, but Slay The Spire. There are tons of cool encounter ideas in that game.
One example is a miniboss encounter: the first action the enemy takes is to give itself a state in which it gains an attack buff every time the player uses a "skill" card (which usually gives the player Block points). After that, the enemy uses either a plain big attack or a weaker attack that gives the player a defense debuff.
Another example is a boss that splits in two when its HP is below 50% HP. Those enemies in turn split in two when they get below 50% HP.
Since not every encounter is a boss, here's an idea for a minion battle: two enemies alternate between a basic attack, a skill that buffs their attack damage, and a skill that debuffs the player's attack damage. The first time the player hits them, they gain Block for a turn.
Slay the Spire is a great source of inspiration, but its mechanics don't always transfer to RM cleanly. Here are some ideas I've had that are specific to RM:
- An enemy that has really high defense, so physical attacks (normally) don't do much damage. This can be due to either a very high base Defense stat, or a state that amplifies their defense. (Bonus: another enemy that is the same, but for Magic Defense.)
- An enemy that uses a devastating attack every 4 turns.
- An enemy that changes its element every other turn on a set rotation.
So you see, there are some great ideas that aren't math-based! Just tweak the values until you get the results you want.