Apart from the History/Background of Gremlin in Classic Enemies, there's only a couple of sentences in 4th Ed Champions Universe about WITCH.
My own supposition about WITCH was that they weren't like all the other supervillain organizations. No fancy uniforms. No high-tech blaster weapons. No VTOL troop carriers. No ranks, or chain of command. They are organized in a cellular structure, with each cell capable of independent operation. They are thoroughly covert, using second-hand stores and other such low-key businesses as their safe houses and headquarters.
They do have supervillains as part of the organization--
The Matriarch--Founder of WITCH, and its guiding force with regards to philosophy and operations. Quite possibly the world's most powerful and versatile telekinetic. Determined to see WITCH fulfill its ultimate goal--the eradication of men from the human race.
Doctor Dynamite--Possessing superhuman strength and Impervious to any physical injury, she wears a harness loaded with powerful shaped charges capable of generating tremendous explosions that she can direct as needed.
Hatchet Job--Former PRIMUS agent who was turned down for Silver Avenger status. She broke into PRIMUS's labs and took the Silver Avenger drugs herself, without physicians monitoring the procedure or waiting the recommended intervals between injections. While she became physically enhanced to the level of a Silver Avenger, her aggression levels increased as well. While she does carry guns and knows how to use them, her favored weapons are twin hatchets which she can use as melee or throwing weapons.
Fire Blossom--A powerful pyrokinetic who can also teleport herself and other by transforming into fire. Her powers came from an otherworldly being who offered them to her so she could protect herself and her son from her ex-husband--in exchange for her "essential being."
Gigantua--Twelve feet tall and built like a sumo wrestler, with strength and density to match. Was a victim of VIPER scientists trying to recreate the process that created Grond. She managed to retain her intelligence, but the permanent increase to her size and weight left her angry and hateful.
They also use other supervillainesses as needed, except for those who have a Code Against Killing.