Intro:
Sizes are in proportion to Player Character Size.
Character in test will be a Warrior Tank kind of character.
Dungeon map can be just a single corridor for first test.
Monster Aggro range needs to be figured out. 
Probably better to only spawn Monster if you get close enough to there location.
I will play Realm of the mad god the next days to check how enemy AI works there.
I dont want to copy alot of that game but i feel like they are doing combat kinda right.


Player Stats
Hp: 100
Atk: 10
Move-Spd.: 100%
Size: 100%
Attack Range: 150

Attack Range: 100 Range = 1x Player Character Hitbox

Leftclick: (Auto Attack)
Cooldown: 0,75 Second

Righclick: (Block)
Cooldown: 15 Seconds
Blocks all damage for the next 3 seconds.

Button 1: Ground Slam
Cooldown: 20 Seconds
Mana: no Mana during first concept Test
Dmg: Atk x 2.5 (25 in this case)
Range: 300 (AoE)
Location: Center of character.

Monster:

Monster A
HP: 10
Atk: 5
Move-Spd: 110%
Size: 80%
Strategie: Runs Towards Player, damage on collision

Monster B
HP: 30
Atk: 10
Move-Spd: 80%
Size: 100%
Strategie: Shoots projectiles with 800 Range, tries to stay 600-700 Range away from player, 1 sec. attack cd

Monster C
HP: 25
Atk: 10
Move-Spd: 95%
Size: 120%
Strategie: Runs towards player, damage on collision


Encounter:
1: 2x A
2: 2x A 1x C
3: 2x B
4: 3x A 2x B
5: 2x B 2x C
6: 5x C
7: 5x B