Archwizard's Might
Level 20 Wizard

Prerequisites: archwizard’s spellcraft

You have mastered the greatest secrets of arcane magic. You
gain an additional 10th-level spell slot.

Metamagic Mastery
Level 20 Wizard

Altering your spells doesn’t take any longer than casting them
normally. You can use metamagic single actions as free actions.

Spell Combination
Level 20 Wizard

You can merge spells, producing multiple effects with a single
casting. One slot of each level of spell you can cast, except
2nd level and 1st level, becomes a spell combination slot (this
doesn’t apply to cantrips). When you prepare your spells, you
can fill a combination slot with a combination of two spells.
Each spell in the combination must be 2 or more spell levels
below the slot’s level, and both must target only one creature or
object or have the option to target only one creature or object.
Each spell in the combination must also have the same means of
determining whether it has an effect—both spells must require a
ranged spell attack roll, require the same type of saving throw,
or automatically affect the target.

When you cast a combined spell, it affects only one target,
even if the component spells normally affect more than one. If
any spell in the combination has further restrictions (such as
targeting only living creatures), you must abide by all restrictions.
The combined spell uses the shorter of the component spells’
ranges. Resolve a combined spell as if were a single spell, but
apply the effects of both component spells. For example, if the
spell’s target succeeded at the save against a combined spell, it
would apply the success effect of each spell, and if it critically
failed, it would apply the critical failure effect of both spells.