-Any Summon (I used finch staff cuz lol)
-Stardust Armor for +5 summons
-Summoning Potion for +1
-Necromantic Scroll for +1
-Base summon of 1
-You'll notice this gives you 8 active summons not nine, but ATTEMPTING to summon (aka using summon one more time) counts for the 9th in the achievement.
-Enjoy