Similar to my reasons really. I feel the -5/+10 invalidates other fighting styles too much. If all the styles got something similar (including unarmed) it wouldn't be so imbalancing. It's probably less work just to remove it though.
Obviously you can do what you like with it, but I think it's just a regular quarterstaff. The Star Spawn Seer doesn't even have the Magic Weapons trait, the additonal effects on the attack are down to the creature, not the weapon.
I'd take Sapping Sting as a base.
Casting Time: 1 action
Range: 30 feet
Components: V, S
Duration: Instantaneous
Str save or take 1d4/2d4/3d4/4d4 force damage and pushed back 5 feet.
Maybe up the damage to d6 as a 5' pushback isn't as strong as Prone.
Not every Warlock, they aren't Clerics. The fluff (and Mike Mearls) supports their powers and spells being learned or permanently bestowed. Down to the DM really.
My players are probably goint to reach the Ziggurat next session, I've been building it with Dungeondraft and using Roll20 bits for the rainbow bridge.
While the new website is nice, is there any chance you might step back from giving away the entire plot of each individual adventure on the Gears of Revolution page?