Htflags

Controls 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.
64 - Sprite will be insusceptible to floor palette of sector containing this sprite. See spritenopal.

It is a bitfield, so add together the values you want and then set htflags to the sum.