A Symbiote

"I call it a Symbiote," the mad witch explained.

"Symbiote? Wait... isn't that like the opposite of a parasite?" the saner witch questioned, "a Parasite only takes from the host while harming it, but a symbiotic relationship goes both ways"

"Well yes... but it works as a Symbiote only for the primary host. Once it latches on, it will copy and learn from them before it starts to spread itself to others, controlling or manipulating them in ways that benefit their primary host. So, it's a Symbiote for the Primary and Parasite for everything else"

"Okay... but what exactly is it?" the other witch questioned.

The mad witch then turned the pages to what looked like an ink stain. Placing a finger on the page, the picture became animated. It showed the inky looking creature moving and slithering around before it approached a person. The ink then lunged at them, enveloping them and transforming them, making them bigger and stronger. Then more people showed up around the main host and various drops of ink separated from the main host before going after them.

"It's essentially a black slime that can be worn," she explained, "should the main host die, the symbiote will merely store their consciousness in itself and then find a new body for its primary host to inhabit"

"So... did you make yourself the primary host?"

"No. That would have been troublesome," the mad witch replied, "however, I can show you the primary host I found"

As she told her partner so, her hand held up a crystal ball. The previously clear ball went cloudy before showing an animated image within.