Enemies, spawning and difficulty

Place a few, spawn the rest

Enemies you place in the editor are good for authored levels, where the same thing should happen every time. For anything endless you want a spawner: an invisible entity whose behaviour creates enemies as the game runs.

• waveSpawner — sends formations in sequence. Each wave names a texture, a count, a shape (line, vee, sine) and how long before the next.
• hazardSpawner — a steady stream of obstacles, weighted so some appear more often than others.
• depthSpawner — the 2.5D version, placing things ahead of the camera and clearing them once passed.

Making them dangerous

Two ways, and they are not the same:

• damageOnTouch on the enemy. It has an invulnerability window, which matters — an overlap fires every frame you are touching, so without one a single contact drains every life you have in a third of a second.
• An On Overlap rule in the graph, when you want something more than damage: a pickup, a door, a checkpoint.

Making them killable

Wire an On Overlap between your bullet tag and your enemy tag, then destroy both, add to the score and burst some particles. That is the whole loop, and it is four nodes:

On Overlap  (bullet, enemy)
  └─ Destroy (self)          the bullet
       └─ Destroy (other)    the enemy
            └─ Add To Variable  score + 100
                 └─ Particle Burst

Difficulty that rises

A game at a constant difficulty stops being interesting in about ninety seconds. The kits ramp in one of three ways:

The simplest version is an On Timer node adding a little to a speed variable every few seconds, with everything else reading that variable. One number, and the whole game tightens.

Clean up after yourself

Anything spawned must eventually be destroyed, or the scene fills with things you cannot see. destroyOffscreen handles the usual case. Bullets should also expire on a timer, in case they never reach an edge.