From Quake Wiki
Scrags (monster_wizard in the QC code) are the only flying monster in standard Quake. Their slime projectiles are easy to dodge, but you'll need lots of room to move and a sharp eye for other Scrags. At long range, use the Shotgun, the Nailgun the Super Nailgun, or the Rocket Launcher. At close range, use a Double-Barrelled Shotgun. At medium range, if you have good aim and are far enough away not to be hurt by the explosion, you can lob a Grenade at a Scrag for a one-shot kill.
Scrags possess some cunning beyond the lofty standard set by the other monsters in Quake. They are constantly moving side to side (except when attacking), and so manage to dodge many incoming slow-moving projectiles. Also, if you duck behind cover while they are attacking, they may throw an extra shot or two at your last seen location, so you might want to be careful before you pop back out again.
monster_wizard is the entity for placing Scrags in a level.
|targetname||The targetname of the Scrag. When triggered, the Scrag will wake up if inactive.|
|target||The targetname of the entity to be triggered when the Scrag dies.|
|killtarget||The targetname of the entity to be removed when the Scrag dies.|
The monster_wizard entity supports the following spawnflags:
|1||Ambush||The Scrag will not wake up from seeing other monsters wake up or hearing sounds.|
It also supports the standard spawnflags for difficulty and deathmatch presence.
|256||Not on Easy||The Scrag will not spawn on Easy difficulty.|
|512||Not on Normal||The Scrag will not spawn on Normal difficulty.|
|1024||Not on Hard||The Scrag will not spawn on Hard difficulty.|
|2048||Not in Deathmatch||The Scrag will not spawn in Deathmatch mode.|
This is the format used by TrenchBroom and Worldcraft. Note that the model(...) parameter is not supported by Worldcraft. This does not include the Monster base class definition, which is also required.
@PointClass base(Monster) size(-16 -16 -24, 16 16 40) model(":progs/wizard.mdl") = monster_wizard : "Scrag" 
This is the definition format used for most old Quake editors, including the original QuakeEd.
/*QUAKED monster_wizard (1 0 0) (-16 -16 -24) (16 16 40) Ambush */
The original name of the Scrag was Duke of Sheol
- John Romero on Twitter https://twitter.com/romero/status/595871727483158528