Htflags

A per-actor property, this controls special flags for sprites. In the following listing, whenever a label for a value is defined in the global CON namespace by default, it is shown after the numeric value:

1 - SFLAG_SHADOW - Generates a shadow. See spriteshadow.
2 - SFLAG_NVG - Turns palette 6 whenever night vision goggles are used. See spritenvg.
4 - SFLAG_NOSHADE - 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 - SFLAG_BADGUY - Is an enemy. See useractor.
64 - SFLAG_NOPAL - Sprite will be insusceptible to floor palette of sector containing this sprite. See spritenopal.
128 - SFLAG_NOEVENTS - Sprite will not be run through event code.
256 - SFLAG_NOLIGHT - Sprite will not emit hardcoded Polymer-based lights.
512 - SFLAG_USEACTIVATOR - needs description
1024 - internal, do not use
2048 - SFLAG_NOCLIP - Sprite will call "clipmove()" with a clipmask of 0, skipping collision detection with other sprites to increase performance. (Specifically, to prevent runtime behavior that is quadratic with the number of sprites.) Useful for particle effects.
SFLAG_SMOOTHMOVE - needs description
SFLAG_NOTELEPORT - needs description

htflags is a bitfield, so add together the values you want and then set htflags to the sum.
This member can also be set using the per-sprite form of the spriteflags command.