Minor ToB Spoiler
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You do realise that the Summon Planater is a ToB ability, and that the Twisted Rune was designed under the assumption that you cannot use said ability yet?
As for Draconis... I used my lvl 34( I do not use Xp cap removers
) Sorcerer and basically caused an overkill.
Draconis only has so much Hp.
That said, the Twisted Rune is a worthy fight, especially if you are facing them for the first time without any foreknowledge.