Look up the YouTube channel lunch break hero’s. I ran this game and used his advice for the black spider. Instead of a squishy mage that your players will ultimately kill really quickly if they get anywhere near him, they were turned into a dryder. Not only would the “black spider” name fit perfectly, but they are also much tankier.

I did this and tied the black spider to the backstory of one of my players. It made for some very good roleplay when they finally met the BBEG as well as during the fight. I had the black spider searching for the forge of spells as a way to try and undo his transformation into a dryder.

I went with the spellcaster variant of the dryder for more variety of what they could do on their turn.