Despawning and Respawning Glitch
The way Chip's Challenge 2 loads levels can cause objects to spontaneously appear or disappear as soon as a level starts, usually by activating another glitch in the previous level or before resetting the level. Such instances of objects disappearing or appearing are documented here.
Vanishing objects
Via level reset during spring mine
In this example gif, Chip spring mines a block off a turtle and resets the level after dying from doing so. This causes the block to disappear once the level is loaded again. The eye is only included for visibility.
See also this gif, which demonstrates that the object doing the pushing does not need to be the player as long as you restart at the right time:
This also works when the entity that is spring mined off the turtle does not match the entity at the start of the level:
Note that moving entities will not be affected if they move as soon as the level starts, which is why the glider in the above gif needed to be enclosed in toggle doors.
Generating objects
All known glitches that generate objects exclusively involve objects being vanished beforehand.