If you're not familiar with the concept of combined arms, it's a form of military organization where different types of weapons are integrated together into units so that they can cover each other's weaknesses. For example, a combined arms formation of tanks and infantry allows infantry to screen for the tanks to prevent the tanks from being hit at close range in their blind spots, while the tanks can provide heavy fire support to infantry if they run up against a fortified position or enemy armor.
I design enemies for Guardian Cry in the same way - each enemy has a distinct niche, and their abilities complement each other to make them more dangerous when combined. I introduce them separately where players can learn and exploit their weaknesses, and then I make the player fight them together.
The enemies in the Guardian Cry demo provide a clear example. Gremlins (the purple rat-looking things that pop out of walls) have a projectile fireball attack that can hit the player anywhere on the screen, but they have a low attack rate, low health, and are immobile. This means that if the player can get close, they're pretty easy to kill.
Fire Snakes, on the other hand, have high health, a large profile, and a short-range spit attack. Their large size makes them difficult to avoid, their spit attack forces the player to pay attention and carefully manage their range and angle of attack, and their high health means they take a bit of time to kill. They're slow and have a low attack rate, though, so they don't present a lot of immediate danger. All this combines to form an enemy that, while not super deadly, makes an effective wall.
Finally, we have Firedancers. These roly-poly lizards barrel toward the player character at high speeds, leaving fire in their wake. Their high-speed charge, and the fact that they make the room more dangerous the longer they're alive, means that they must be dealt with quickly. However, alone, they're easy to manage - stand still, let them roll toward you, then hit them with your sword when they're close enough.
Now we apply the principle of combined arms. The player enters a room. There are gremlins on the far wall, Fire Snakes in the middle, and Firedancers that charge the player. The Firedancers create a threat that the player must immediately deal with. The player cannot simply stand still and hit them as they come because the Gremlins are launching fireballs that must be dodged. The Fire Snakes creep toward the player, slowly constricting the area in which the player can maneuver, which makes it gradually more difficult to both dodge the fireballs and the Firedancers. All of this comes together to form a demanding encounter from simple, complementary pieces.