Help with Wizard boss battle

[tim01300]

So after a long two years my group is finally nearing the end of my campaign. They have been chasing after an evil mage and will finally get to confront him. I need help knowning if I'm balancing this correctly. I don't have tons of experience with high level mage fights.

The party was supposed to be around level 19 when we finished, but due to deaths and time constraints its a much weaker party. The players are not power gamers by any means.
The party consists of a druid (lvl 15), another druid (14), barb (12), fighter (12), monk (13) arcane archer(12).

Throughout the course of the campaign I've shown this boss wizard using high level spells, such as wail of the banshee. I've dropped him to level 18. Because this is the final boss in the campaign I'm also planning on having him take two turns per round and I've buffed up his FORT saves a little.

But my concern is that my players can't deal with this fight, and I don't want a party wipe for my finale. Round one prismatic sphere, round two wail of the banshee (Save DC 25) and I think I'll have a bunch of sad fellas at my table.

The final encounter is them trying to stop his ritual of ascending into godhood by draining the elven god trees power (its the final fight from baldurs gate two basically)

Thoughts? Any help or ideas would be appreciated.

[Eurus]

I pretty much can't think of any way for that party to handle a level 18 wizard in a fair fight, so you're probably going to have to figure out some sort of plot device artifact that they can use to either weaken the wizard or empower themselves.

[tim01300]

An artifact from the elves isn't a bad idea, something to help with spell saves.

What level mage do you think IS appropriate/fair for this group, considering that its the final fight of the campaign?

[Eldariel]

An artifact from the elves isn't a bad idea, something to help with spell saves.

What level mage do you think IS appropriate/fair for this group, considering that its the final fight of the campaign?

Honestly, if you play the Mage to their ability, depending on the party's magic item array and particularly the Druids' spells, even a level 15 Wizard could be a TPK (hell, perhaps level 13). Level 17 brings stuff like Shapechange, Gate and Time Stop to the table doing ugly, ugly things to action economy, character power and so on. Shapechange, among its billion uses, enables the Wizard to legit take two turns in one for instance (turning into e.g. Chronotyryn [Fiend Folio] or even just core Choker (http://www.d20srd.org/srd/monsters/choker.htm) - and then after casting twice, he can use the free action to turn into something else at the end of the turn). Gate just throws some Pit Fiends or Balors at the party (from the lower end of the powerscale; you could also use epic monsters like Phane (http://www.d20srd.org/srd/epic/monsters/abomination.htm#phane) or Infernal (http://www.d20srd.org/srd/epic/monsters/abomination.htm#infernal) for 20+ rounds with some caster level boosting items like Orange Prism Ioun Stone (http://www.d20srd.org/srd/magicItems/wondrousItems.htm#iounStones) or Beads of Karma (http://www.d20srd.org/srd/magicItems/wondrousItems.htm#strandofPrayerBeads)). It's all about how many of the more broken spells (Simulacrum? Planar Binding? Magic Jar? Animate Dead?) you're willing to have Irenicus utilise, and how much effort he's put into those.

You could have him utilise all sorts of underlings before they face him and only have him be accompanied by something minor like a Zombie Dragon or something in the actual fight. Shapechange & Gate are probably so strong that if used to anywhere near their limits, they would defeat the party alone. If the party sees him use Wail of the Banshee, drop tips that the fight is coming and have them prepare: Druids know Death Ward among other things so it's not like they have no options.

[flappeercraft]

What I would do in this scenario is just cheap out and just make the PC's find a 1 charge artifact that when used it gives all the PC's an extra level or 2 just to balance it out. A wizard 18 is too powerful for your current party if played well and even if not played well he can still probably beat them anyways but they would have some small chance.

[Kelb_Panthera]

There's not enough information for us to help you here.

How do the druids behave and what do their standard spell-loads look like?

What's in the wizard's spellbook?

This is doable but we've got to know what we're working with.

[NecessaryWeevil]

It's commonly accepted that fights against single foes are swingy: either the party defeats him handily or he wipes the floor with them. So don't do it.

He's casting some crazy ritual, right? So maybe it's a long ritual and if he turns away to fight the party, the forces involved will tear him apart. Therefore, make them fight several of his minions while he conducts the ritual. But give them a time limit or something: down the minions in X turns or he completes the ritual. Or, break through the minions to land hits on the boss, forcing him to make increasingly difficult concentration checks. The party wins when he fails and explodes.