Xykon

Enhanced Metamagic

Energy Drain is a 9th level spell, Maximize requires a spell slot at least 3 levels higher. Meteor Swarm is also a 9th level spell, and Still requires a spell slot at least 1 level higher. Hence these spells would require a 12th level and 10th level spell slot, respectively.

There are multiple ways for Xykon to achieve this.

Improved Spell Capacity x3

This feat, taken three times, gives Xykon a 12th level spell slot to use for Energy Drain, and implies a 10th level spell slot for Meteor Swarm. Xykon also needs the Epic Spellcasting feat to cast Superb Dispelling, so this requires he be at least 26th level. This gives him two epic feats at levels 21 and 24, as well as two bonus Epic feats from his Sorcerer levels, at levels 23 and 26.

Improved Metamagic

This feat would reduce the cost of Maximize down to 2 or even 1 level higher, but not 0, so Xykon would still need at least a 10th level spell slot. It requires at least rank 30 in spellcraft, so implies a level of at least 27th.

Sudden Maximize or Sudden Still

With Sudden Maximize, once per day, Xykon could maximize a spell without increasing its spell level. He doesn’t need to decide in advance which spell or when to use it. Likewise for Sudden Still. This brings Xykon down to 21+, since he still needs Epic Spellcasting, but Rich has told us that his level is higher than Serini’s, and Serini is “low epic,” hence 22+ is a floor in this case.

Choosing

Throughout the Vaarsuvius vs. Xykon fight, the comic consistently explains unusual mechanical outcomes.

One of the soul splices explains that Chain Lightning doesn’t hurt Xykon because liches are immune.
Xykon explains that he built a magic item to protect himself from his own Meteor Swarm.
Redcloak explains that his caster level is not high enough to dispel Vaarsuvius’s buffs.
Xykon explains that O-Chul can’t destroy the phylactery because it is protected by abjurations.

When V casts a Quickened Chain Lightning, Xykon implies V used a 10th level spell slot. Xykon later casts the Maximized Energy Drain and Still Meteor Swarm, but no alternative mechanism is mentioned.

If V’s slot-based explanation is meant to carry forward to Xykon’s spells, then it seems to favor Xykon using sufficiently high spell slots rather than one-off metamagic shortcuts. That favors the Improved Spell Capacity route.

Dodge and Deflect

In panel 6 of comic 653, Xykon avoids a Disintegrate with a “deflect!” sound effect. In panel 13 of comic 652, he avoids a different Disintegrate with a “dodge!” sound effect.

“Deflect” evokes a deflection bonus, a common named AC bonus. Within that context, “dodge” can likewise evoke a dodge bonus. While these work as allusions to the rules, there is no evidence how Xykon is acquiring these bonuses.

Reverse Psychology

In Strip 106 Redcloak mentions Xykon having ranks in Reverse Psychology. Although delivered as a joke, it is a clear statement about Xykon’s skills. We know less about it than most such jokes, since Xykon himself refers to making a Bluff check a few panels earlier. Perhaps 5 ranks gives one a synergy bonus?