Add in different types of enemies, other than the ones that simply chase the player.
Firstly, 'slimes' would move in a set pattern, probably back and forth along a path. These would get turned around by walls, or else move a set distance (something like 3-5 spaces, max) then turn.
Another possibility: 'ghosts' would move in circles, but they would be able to move through walls. For added difficulty, they could 'disappear' while inside a wall, meaning the player would have to be extra vigilant to keep track of them.
With the addition of these new enemy types, it may be necessary to redesign the layout of the level - increase size, adjust enemy spawn locations, etc.
I may also want to consider making it so that some of the monsters move independently of the player's movements - their steps would be triggered by timers rather than key events.
Add in different types of enemies, other than the ones that simply chase the player. Firstly, 'slimes' would move in a set pattern, probably back and forth along a path. These would get turned around by walls, or else move a set distance (something like 3-5 spaces, max) then turn. Another possibility: 'ghosts' would move in circles, but they would be able to move through walls. For added difficulty, they could 'disappear' while inside a wall, meaning the player would have to be extra vigilant to keep track of them.
With the addition of these new enemy types, it may be necessary to redesign the layout of the level - increase size, adjust enemy spawn locations, etc. I may also want to consider making it so that some of the monsters move independently of the player's movements - their steps would be triggered by timers rather than key events.