And it didn't go all to well. Any tips on how to defeat him solo with a nec summoner are very welcome.
A few things I can add:
1/Bind Left mouse to summon Shadow - , when you need to move, right mouse will be Bend the Shadow. you can shift Left mouse to summon them then right click Bend the shadow, it's just like teleport now.
2/The Dark Circle Baal creates under your feet will explode after 3-4 second, deal heavy damage, with too many minions, will be hard to see and dodge.
3/D-Baal IS HARD, don't try him until you can kill Mephisto/ Diablo within 10 second (so if he summons them, you can kill them fast enough).
I suggest 2 solutions:
1/If you don't want to switch to fighter build, farm until you get Uber gear for act 5 Mers. He is great for fighting D-Baal. You can go with only your mers, try dodge the Black circle until he dies.
2/Just farm more item to get Uber damage for your army (there are items for Necro that grant Kraken Stance and enhance stance radius as well). With 100+ minion with Kraken Stance buff, and 2 S-max buff totems, You can definitely kill Ball's minion faster can he can summon.