When a game is staring, people start earning coins (like an iron generator on bedwars but those are coins on a kind of bank account. In your inventory you have a wooden sword, 2 shops and settings. This is an example map to understand better what I mean here: https://builtbybit.com/resources/tower-defense-minigame-map.39591/
When a mob reach the end of the map, it damages the castle and when your castle is at 0 HP, you've lost the game. I'm making a quick explanation of what I want here, but on this video you can see what plugin I want: https://www.youtube.com/watch?v=gn-h1h63irI
A mob is a monster like zombie. You can upgrade zombies. You can upgrade your mob in game (that cost exp) and for example the zombie will get leather, iron gold or diamond armor (for esthetic) or a giant zombie for example, but the mob will get more HP and competencies like the ability to be invisible for some towers.
Tower
A tower is a structure of 3x3 or 5x5. You have different type of tower, one will launch arrows, the other one will put boombs on the ground (represented by a boomb skull on the ground), an other tower that will slow mobs or freeze them.
Wooden sword
With that sword which is upgradable (I will talk about this later), you can only damage enemies on your side. When you hit some mobs, you are loading an ability. The ability of a sword may be something like when you're right click on hit you have tean arrows launched when you look.
First shop
On this shop, you can buy mobs. You can buy up to x mobs (that is configured in arena setup) and you have to wait x seconds (that is configured in arena setup too) between each waves. When you buy that mobs, send are sent to enemy side. When the enemy kill one of your mobs, you earn EXP (configurable at each mob setup).
Second shop
On this shop you can upgrade many things, like your sword (wooden to iron etc..), you can upgrade your money. Imagine that before, you won 10 coins/sec. So for 200 coins you can win 30 coins/sec (everything is configurable in configs).
You can buy potions. A potion will give effects to mobs, for example you drop a potion on the map, and if it's ennemy mobs (so on your side), every mobs will get fire damage. Or "positive potions" that heal your mobs (so you have to drop them in enemy side)