Spriteflags

spriteflags <value>

Sets special flags for sprites. The values are:

1 - Generates a shadow. See spriteshadow.
2 - Turns palette 6 whenever night vision goggles are used. See spritenvg.
4 - The sprite's shade is unaffected by the shade of its sector. See spritenoshade.
8 - Is a projectile.
16 - Prevents teleporting. The sprite is not entered into the decal deletion queue.
32 - Is an enemy. See useractor, but note that this is distinct from setting the useractor type to either of the enemy types.
64 - Sprite will be insusceptible to floor palette of sector containing this sprite. See spritenopal.
2048 - Sprite will skip x/y "clipmove()" . This skips objects checking for collisions with other actors to increase performance. Useful for particle effects.

It is a bitfield, so add together the values you want and then use spriteflags with the sum.

Outside of actors and states,
spriteflags <picnum> <value>
sets the same flags per-tile. When a flag is checked, the per-tile value is XORed with the per-sprite value, i.e. one reverses the other.

Flags that are not explicitly listed may be reserved for internal use.
The actor member htflags is modified with the first form of this command.