Looking to make a boss monster, need some advice/help
So in my world there is a highly intelligent goblin shaman that's cripple, and thus he rides on the shoulder of a troll for protection. They have a strong bond, the shaman blesses the troll with spells and the troll is the dumb brute of the two protecting the shaman.
I'm designing a fight for when the party encounters the duo, they are currently 5 lvl 4 players but will probably be lvl 5/6/7 at the time of the encounter. Anyone know what kind of monster mix I should use? Also should I let the players be able to target the shaman riding on top with ranged attacks? Or let the duo be one entity? I'm not sure in terms of balance.
Never designed my own monsters so that's why I'm reaching out!