Impulse 12 is known as a "limited gimmie" and is relatively similar to impulse 9. It is limited because it does not give the player the two Keys. It also brings up the Thunderbolt instead of the Rocket Launcher. Impulse 13 can give the player the Silver Key, while impulse 14 can give the player the Gold Key, meaning all three will result in a similar effect to impulse 9.
Impulse 252 will give the player the Pentagram of Protection (Satan mode: ON!), impulse 253 will give the player the Ring of Shadows (You can do that? Cool. -Bond), and impulse 254 will give the player the Biosuit (Suit up!). All three last for 30 seconds and don't play any of the sounds of the normal Powerups, instead giving precache errors. This could potentially be fixed according to Sean Dunn, but would result in more memory being used, meaning he felt the errors were a necessary evil to cut back on memory.