We have never thought that level design can be so hard to balance. As first time game designers, object placement and enemy positioning is vital. Defining difficulty also signify player retainability. After a few reads and topics about level design, we have listed our takes and approach on monster or enemy placements.
These are monsters that teaches game mechanics. This monsters are predominant in the begining of the game, but it can also appear on the later part if new game mechanics are introduced. These monsters are helpful since they clearly demonstrate the effects of the new mechanics.
These are weak monsters that help users practice the game mechanics. It is not as obvious as mechanic monsters but likewise it is a small fry for users to enjoy killing.
The mechanic test. These type of monsters test user and is usually placed in the end of each level or region.
Unpredictable monsters are risky and double edged. Although it introduce variety it also presents unpredictability.
A difficult monster doesn't mean a challenging game. This is one of our common mistake, we believed that puting hard monsters can put some flavor or interest in our game. It is not how difficult the monster is but how we make players perform our game mechanics.
Placement tells the pacing. Developers can calculate or predict the player's engagement through a properly designed monster placement. Being able to predict the players interaction is vital to maintain player retainability.
A boss monster is a test of mechanics. The position of the boss monster is at the end of each level to test the player's understanding of that mechanics introduced or is availble in such area.
Know your engagement area. Ensure that you have control on the area that the player and the character interacts. This reduces the risk of unexpected bugs due to behaviour glitches.