So I've been working on an infinite level generator, and it works like this:
There are spawner objects all around the player. If they are active, they spawn the tiles as you run. They become active under 2 conditions
Condition 1: If the spawner is not currently overlapping an existing tile
Condition 2: If the player is running in the direction of the spawner. So the right spawners are only active when the player is moving right, bottom are only active when player is falling, etc.
This leaves 1 big problem, the tiles look a little odd when they are placed like 4 pixels above the one next to it, or 25 pixels apart, making the player think they can squeeze between the gaps. It's on the Level 2 Sheet, events 16-43 in a group called NewGen