Defender 2

Defender 2 -- ARC (Atari UK, Ltd)

Type RAVEN while playing. This unlocks the following keyboard cheats:

I - toggles invincibility
N - Teleports you to the next level

Type GOATY to become invincible.

Here's some level codes:

LEMAC, ZIPPO, LAZER, DAFAD, MAMOG, FUNKY, and DONKY.

List of cheats