The lich's phylactery is the +5 vorpal greatsword the party took as loot

Well now I'm not going to cast any spells for you.

Hmmmph!

Senile immortal skelly
Must have forgotten his jelyl
Now he's a bitch lich
Can't scratch that adventurin' itch

...

Phun With Phylacteries

I'm stealing this, thanks a lot(h).

>The lich's phylactery is a random object floating inside a bag of holding

How the fuck did the party beat a Lich Capable of casting Epic-Level spells?

Lrn2Lich, that custom Phylactery shit only applies to people with an epic Netherese spell, owned by a fat bloated netherese fuck no one knows about, and Lichthralls.

Even then, the modern application in 3.5 of Lichdom was slowly putting one's lifeforce into the Phylactery as it was constructed in 3 stages, gaining undead qualities as noted throughout the edition's run with the foreign school of necromancy, Necromancer variat, Pale Mastery's and Deathwalker class features, Orcus's newly aquired ability to shift between an undead-like form and his more fleshy goat/boar hybrid form before finally making the connection to the plane of negative energy and becoming undead as a result, the prime factor noted in multiple writings of Van Richten, the "Obscure" part of the ritual being the actual process in which one's soul is unhinged from the body for Phylactery placement, which is a process still mentioned in Van Richten's guide, though one of many, involving the poison and the bit of Lichdom that earns it it's "evil" descriptor, or at least causes the according alinement change to suitor it on a meta level, I.E Kharlat Jharegs fuckup in NWN.

Anyhow, even by that stage the Lich has access to Lich Power rituals, his set of Salient abilities (Still canon, see Monsters of Forgotten Realms and Van Richtens guide to liches for cross-reference) earned by age category.

Now then, polymorphing the object or acquiring the services of a transmuter are completely in the realms of the possible though, so you have whatever expansive rules such things offer.

But still, if you want to follow up where 2e left off and 3.5 implied continuation but barely covered it, Sword and Sorcery did conversions of Lich Age categories to 3.5 in their Ravenloft works, you'll still need the other stuff though.

And again, broke-ass Lich power rituals, and unstatted demilich powers in Forgotten realms canon.

>he's gonna get shanghaied as our new mage

This. We're keeping the sword. We're keeping you. Better learn some buff spells!

As for the broken ass shit you get by being a Lich:
>If specialist Wizard, you no longer have a prohibited school and can learn any spells from that school because all the time in the world, you still have the features of your specialization though
>Lich Specific artifacts only you can craft, like a ring and crown that steal stats from the person who dies with them equipped.
>Lich unique spells
>Salient abilities
>Abilities by age category (these are now applied as templates that build on your base) And enhanced undead and Spellstiched to boot
>Can see through the eyes of your skeletals, though a giveaway is their sockets glow the same as your own
>Can designate a single undead with a blessing of sorts, similar to that shit a level 3 master vampire does, and control said undead with more complex tasks
>Paralytic touch looks like you instakilled people, and the fear aura makes em flee, so context wise, the DM needs to tell PCs unaware of what the Lich does said person is dead if they didn't make any of that heal roll shit, and that's a free cadaver for you
>Fucking Power Rituals, aquired by your connection to the Negative energy plane like the fucking touch of god
As a note, Accerak and Vecna are highly hinted at having used these, Vecna did so in his original conquest on Oerth, and used a Custom Dweomer/Epic spell that blended a power ritual with other things to achive godhood, before Kaz belw him up during the process of ascention, and Acceraks was an admixture of a gained Demilich ability and a power ritual extended to Epic spell.

The lich's phylactery is secretly hidden inside the chest cavity of a mirror golem; which has just ambushed your party. The mirror golem is immune to magic based attack, and can reflect ranged magical attacks. The golem can trap creatures inside it's mirror shield. What do?

Anyhow, on the jesus fucking shitfuck christ shit Demiliches can do:

You remember that False Body crap Kangaxx did in BG? yeah, that's actually a canonical ability, except it's MUCH WORSE THAN YOU COULD IMAGINE.

You see, Demiliches whilst astrally projected, can literally designate up to 100 undead to have their fucking old Template and stats they had before becoming a Demilich on them. Yeah, that's right, 100 liches at once, hopefully distributed around the planes to start up cults to the Demilich in question mind you, or are working on other projects.

The next power is the ability to contact -any- evil outsider, It was stated the DM would have to stat this, so how it officially works is unknown, other than "Hey Orcus, want to borrow 50 of me at my peak in the Blood war?" in addition to this, said outsider is outright compelled to do what you say.

The third power? the Demilich can literally do some Bloodborne Realm of Nightmare shit and cause natural disaster on a single plane at a time, earthquakes, tsunamis and Tornadoes are all on the list here, but that isn't the horrible part. You see in 3.5 there's a fucking weather condition called black rain, a rain that shows up on the anniversary of a gods death or some other depressive event, and guess what it does?
It prevents ALL forms of divine spells being cast.
And now the Demilich has control over the fucking weather and an army of clones capable of raising an army, not barring the servants they garner or make (Lichhthralls and vassaliches) in the process of this.

The fourth power? Basically, a demilich can ride a dead corpse and pilot it as though it's old body.

Don't forget to apply the Lichthrall template to the golem.