Help make me invincible.

[Testament]

Invincibility? Shapechange into a Shambling Mound and have someone poke you repeatedly with a Shocking Weapon. Hello infinite Con!

Seriously though, the suggestions here are all good. And Abjurers have possibly the most dangerous assasination spells around now, Duelward and Reciprocal Gyre. Gyre in particular is a real Cleric hater, or buffed-beastie crusher.

And rods of Extend are your friend.

 

[domino]

Well, while it doesn't make you completely invincible, it never hurts to be incoporeal and invisible.

And not there.

 

[Ringmereth]

You mean a persistent antimagic field? That's a 12th-level spell. Good luck with that one.

As I said before, you can't make an invincible character. No one can. It is impossible.

(Not even the Elminster designation would help.)

Well, yeah. The full build, called the 'Cheater of Mystra', uses Divine Metamagic to get that. Here's one variation of it: Cheater of Mystra.

Anyway, as you said, no one's completely invincibile. But you can come very, very close, especially if you can get Divine Ranks. If not, there's always a way to protect yourself from a foe, given advance warning, spellcasting capability, and some money to work with.

 

[Merlion]

Well, yeah. The full build, called the 'Cheater of Mystra', uses Divine Metamagic to get that.

More proof Divine Metamagic is crazy