Oracle error "too many values", must be solved with nested SELECTs
Using a join?

SELECT 
  minion.boss,
  emp.name, 
  minion.minion
FROM acg_employees emp 
JOIN    
    (SELECT b_id as boss,
                 LTRIM(MAX(SYS_CONNECT_BY_PATH(e_id,','))
                 KEEP (DENSE_RANK LAST ORDER BY curr),',') as minion
    FROM (SELECT b_id,
                 e_id,
                 ROW_NUMBER() OVER (PARTITION BY b_id ORDER BY e_id) AS curr,
                 ROW_NUMBER() OVER (PARTITION BY b_id ORDER BY e_id) -1 AS prev
          FROM acg_boss_of)
    GROUP BY b_id
    CONNECT BY prev = PRIOR curr AND b_id = PRIOR b_id
    START WITH curr = 1) minion
ON (minion.boss=emp.e_id)