True Polymorph is overestimate.
True Polymorph
"If the spell becomes permanent, you no longer control the creature. It might remain friendly to you, depending on how you have treated it."
The Wizard lose the control and It
might remain friendly to you.
Are they friendly to you when you want to turn them into Minions, Controlling them?
Also, they are friendly(or not) to you, not your allies.
And above all, It has no obligation to follow the Wizard's orders.
You have a big problem here.
Wanting to turn creatures into minions is very dangerous. I bet this wizard dies in a week.
Do you want reliable minions?
Finger of Death is the best pick
and again, he's inferior to any sorcerer, with Twinned Finger of Death. Level 20 Sorcerer can create 8 permanent controlled Zombies, while Wizard 4.
Turn them all into you with Distant Seeming Spell and cast suble/psionic spells for Improved Mirror Image without know who is the caster.
Who knew, the sorcerer is the best Necromancer.
Do it at level 14.
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