Satyrn
First Post
That's a good question...I always start with classes or the builds in the back of the MM for my 'phb race' antagonists... maybe I shouldn't. I would love to hear how you would do it different. Maybe that is the problem by making him a warlock/druid instead of just a monster that CAN do things...
This is how I've been making my legion of fiends. They're sort of a cross between monster and NPC, but they work fine as an example since I essentially start with "devil grunt" as a race.
But were I making your druid warlock, I'd follow the same steps
1) I set all their ability scores at 10 or 12, because they're really not worth thinking about and no one but me will ever see them. But if a strength or weakness leaps out at me, I'll knock the score up to 16 or more, or down to to 6 or less.
Randy would get a Wisdom and Charisma of 18, and the rest of his stats would be 12. (If he needed a weakness, I'd drop his Strength, but I don't see it as necessary)
2) For his attacks, I'd just give him eldritch blast, and some other interesting warlock area attack spell. For his traits, I'd give him the ability to summon some strong magically enhanced* critters, and the abilty to wildshape into those same critters (and the ability to cast while wildshaped). I'd also list a decent assortment of spells to remind me that he has options beyond the statblock.
And that's that.
No, There's more. Since this is a boss, I'd consider giving him something akin to legendary actions in the form of a couple custom spells that are cast as a reaction. (A player wanting to learn these spells would have to quest for them, maybe making a pact with Randy's patron, too, along with other onerous tasks that effectively put the spells out of reach).
And Lair Actions. If Randy's in his grove or the like, he'd have been performing rituals to make his home fight back.
I think that should feel like a powerful warlock/druid when encounteredand I'd be happy with that.
*Like, bump up the brown bear to a CR worth fighting. More hit points maybe, but certainly have it's claws bristle with primal might (a couple extra dice of damage) and its bite . . . its bite inflict hex because a warlock's gotta have hex somehow, right? That hex, by the way, would benefit the bear and Randy, so the more bears Randy conjures, the more PCs he can hex, and the more targets he has to choose from.