BBE level 20 gestalt battlemage build?

[Dreadfull]

I suddenly realised i left a few holes in the situation my party is currently in and don't have any prep time left. I thought i still had a week to make this guy but he might need to pop up tonight.

Flavor wise he's like this: A warlord that ruled over an ancient kingdom covering most of the continent the town is on. He reigned through battlefield supremacy and excelled in both magic and physical combat skills.
He was smart enough to have the core of his realm know constant peace but the borders were always at war unless the ocean was reached. he wanted to dominate the entire world eventually but never got around to it as he didn't manage to finish the continent before he was entombed alive below the city the PC's are currently in. And his tomb has been long since forgotten. The town is flooded because PC actions and this caused them to meet the crypt guardian and hear of their impending doom a lot sooner than expected. So he's gonna pup up alone, wet, angry and in a world he barely recognizes.

I have about 15 min to build this guy later on today and hope you guys can help me with some suggestions for builds and maybe a few ideas for legendary actions and magic items.
So, including all current UA and splatbooks, what would be the ultimate build for a gestalt battlecaster BBE?
This guy needs to be able to hold his own against a party of 11th level players for at least a few rounds. The party is well balanced and we have a few munchkins in the group. That's why I figured lvl 20 and gestalt are kinda required unless i want to go epic level.

[Dork_Forge]

I suddenly realised i left a few holes in the situation my party is currently in and don't have any prep time left. I thought i still had a week to make this guy but he might need to pop up tonight.

Flavor wise he's like this: A warlord that ruled over an ancient kingdom covering most of the continent the town is on. He reigned through battlefield supremacy and excelled in both magic and physical combat skills.
He was smart enough to have the core of his realm know constant peace but the borders were always at war unless the ocean was reached. he wanted to dominate the entire world eventually but never got around to it as he didn't manage to finish the continent before he was entombed alive below the city the PC's are currently in. And his tomb has been long since forgotten. The town is flooded because PC actions and this caused them to meet the crypt guardian and hear of their impending doom a lot sooner than expected. So he's gonna pup up alone, wet, angry and in a world he barely recognizes.

I have about 15 min to build this guy later on today and hope you guys can help me with some suggestions for builds and maybe a few ideas for legendary actions and magic items.
So, including all current UA and splatbooks, what would be the ultimate build for a gestalt battlecaster BBE?
This guy needs to be able to hold his own against a party of 11th level players for at least a few rounds. The party is well balanced and we have a few munchkins in the group. That's why I figured lvl 20 and gestalt are kinda required unless i want to go epic level.

Off the top of my head, throw at them a straight 20 Eldritch Knight/Wizard War Mage gestalt and Tough as your base. From there it depends how bad you want this to be for them, you can give him Warcaster and Sentinel and have him zip around the battlefield via teleportation wielding a shield and a magic sword.

The mixture of spell casting and action surge (with the teleportation feature), with high hitpoints, AC and reaction defenses would make him incredibly formidible and fits your theme.

What does your party consist of (race/class and items) so we can better judge how tough to make him?

[CheddarChampion]

If going for power:
Conquest Paladin 20 / Sorcerer (draconic/shadow/divine) 20 - if it doesn't break the flavor.
Auras, smite, extra attack, IDS, scornful rebuke, paladin capstone, metamagic, sorcerer subclass stuff.
Get max charisma, mounted combatant, shield master for evasion-lite, use a lance and a shield.
Secondary priorities: max strength, warcaster, resilient (constitution).

Quicken a fear spell then ride a griffon in to attack.
You can smite on every attack but that will probably be too much damage for a party to handle.

For the Gestalt part, do you get 10 total ASI's/feats?

That aside, you could just make a guy with:
20/14/16*/20*/14*/14, 20d10 HD, extra attack (1), spells as a 20th level wizard (focus on multi-target spells), spell resistance, 20 AC, two turns per round (only one of which can cast a leveled spell), eldritch strike (EK), and war wizard subclass abilities. * = proficiency in saving throw type, give em athletics proficiency too.

[Dreadfull]

Off the top of my head, throw at them a straight 20 Eldritch Knight/Wizard War Mage gestalt and Tough as your base. From there it depends how bad you want this to be for them, you can give him Warcaster and Sentinel and have him zip around the battlefield via teleportation wielding a shield and a magic sword.

The mixture of spell casting and action surge (with the teleportation feature), with high hitpoints, AC and reaction defenses would make him incredibly formidible and fits your theme.

What does your party consist of (race/class and items) so we can better judge how tough to make him?

Eldritch knight/warmage sounds great. your entire suggestion is actually pretty neat. Huge thanks.

The party is a human monk path of the astral self, a firbolg wildfire druid, a goliath forge cleric, a half elf drunken master monk, a minotaur hunter ranger and a halfling war mage wizard.

[chando]

You will probably have a esier time running and making him just deciding what you want from him as a NPC stat block rather than building as a PC. PC's have numerous abilities to make them keep standing, lasting more, going nova, that if used aggainst a party could very well play like a nigthmare.

Pick up a few non-concentration buffs and add them to the stat block already if he is gonna have them acctive when he faces the pcs. Stuff like mirror image.
Eldritch Strike. (The EK ability)
Give him Legendary Action 4. a) Cast a spell (cost two actions). b)Make an weapon attack c) Teleport up to 30 feet.
Givin him warcaster and he will be casting spells at players with save disavantageand the ability to cast a spell as a OA via warcaster. Be merciless with your spells.
Give him Multiattack. Fulano makes four weapon attacks and casts a spell. (before or after the attacks)
Give him both ranged and melee weapon combat capability. Casting a Battefield Control Area spell at players at distance after using your bow/javelin/crossbow attacks to give them disavantage to the saves. With some spells it migth even spell TPK, but a final battle with the BBE probably should have that risk, and PCs have eneght abilitys that make them going down and going back up not so dificult, and they migth have acess to any/all boosts like bless, paladin aura, circle of power, damage resistance...
think of his personality, would be more inclined to face the party in melee with a great wepaon? With a shield and a rapier and precise crit strikes to paralyzed targets?
Does he really need high level wizards spells to be threatning? If he gets all that and simulacrum, Mass suggestion, Meteor Swarm and forcecage on the party, might be a little bit overkill... Mindblank and other protection spells are great.
His simulacrum should probably not get legendary action if you go that route (or just share them with the main one) mainly for simplicity, and will probably only last a round or two.
Have a fire immunity magic item or fireball immunity (i think there is one that gives you immunity to two spells, make that and counterspell/dispel magic?) and throw fireballs all over the place just for the hell of it.
If you do to much things that take the players out of the fight it migth be unfun... but hold person + attacks players goes down in one round its great puts the fear in their hearts and the player will likely get up next round... but dont abuse it.
think of a few tatics before hand.

Round 1 Ranged attacks and Slow.
Legendary attacks attacks and them cast fireball
Round 2 Hold person + Crit attacks.
Legendary actions. Teleport, ranged attacks, spell:?
Round 3 ...

[Dreadfull]

lotsa things

That's a good alternative. The BBE probably needs to be ready for anything. He would attack both ranged with spell and close combat with melee. Warcaster would be vital. I'll be home in an hour and at that point i gotta eat, build the BBE and leave for the session. So which statblock would be a good base?
Other than that, unless the PC's are gonna be stupid (50% chance) the BBE will mostly draw time to get ready to leave and get a bearing on the world or drive the PC's off without killing them because he thinks they are lesser and might make good subjects.
If they are gonna be stupid though there needs to be a suitable showdown. I always use strat with my enemies and make them think about their actions. But yeah limiting what they can do is a given as i don't mind killing one or two of them but a TPK would prevent them from being revived and is to be avoided.

Also lotsa things
It kinda does break the flavor, but im the DM i can always reflavor.

On the gestalt 10 ASI's, NO 10 ASI goes too far. He's got to be a challange. I'm not trying to kill my party, just make them feel this is really really hard if it comes to a fight.

On what you said about just making a guy that does X, yeah you and chando bringing that option up makes me seriously consider it. Thanks fo rthe idea.

[Damon_Tor]

First of all, do not build him as a PC.

Begin with the Warlord statblock and give him spellcasting, dial back his physical stats a bit and buff whatever mental state you want to base his spellcasting on. Maybe give him the Eldritch Knight ability to attack as a bonus action when he casts a spell.

That's pretty much all you have to do.

Edit: so reviewing the statblock, I noticed his Cha is already 18. I'd say dial that up to 20 and dial his con down to 16 (and adjust his hp accordingly). And you should be good to go.

Don't go crazy with spells, the Warlord is already CR 12, techinaclly a bit tough for a level 11 party. I'd give him self buffs and direct damage with some anti-magic defenses and not too much reality warping.

[JNAProductions]

Seconding those who say "Build as an NPC, not as a PC."

PCs and NPCs are built along different lines, intentionally. Use that to your advantage.

[Rukelnikov]

Make him a straight Fighter/Sorcerer 20

This allows you to cast a high level spell and make 4 attacks every turn. The chasis of both classes are strong enough that it doesn't really matter which subclass you take, I'd go for flavor in them.

You would have a total of 12 ASI's to distribute (13 if Vhuman), Warcaster is kind of a must have, and I'd recommend giving him Lucky, Resilient and Tough. Solo creatures need all the resistance they can in order to survive, specially if they don't get Legendary Actions.

Finally, consider when making his statblock, that someone who reigned for as long as you said, in a kingdom as large as you imply, and who is inclined to directly participating in combat, will have spend many of the resources of the kingdom in powering himself up. I'd give him a +2 to every ability score for the tomes he gathered and used during those years.

[Geodude6]

You might like to use the mage fighter NPC (https://www.dandwiki.com/wiki/Mage_Guardian_(5e_Creature)) created by a user of the D&D Wiki. It's CR 17 and has access to 6th-level spells and three attacks per round. If that's not strong enough for you, there are the more powerful variants of mage hero (https://www.dandwiki.com/wiki/Mage_Hero_(5e_Creature)) (CR 19) and mage champion (https://www.dandwiki.com/wiki/Mage_Champion_(5e_Creature)) (CR 23).

Alternatively, you can just use the Warlord statistics and add on spellcasting, as other users have suggested.

[Dreadfull]

You might like to use the mage fighter NPC (https://www.dandwiki.com/wiki/Mage_Guardian_(5e_Creature)) created by a user of the D&D Wiki. It's CR 17 and has access to 6th-level spells and three attacks per round. If that's not strong enough for you, there are the more powerful variants of mage hero (https://www.dandwiki.com/wiki/Mage_Hero_(5e_Creature)) (CR 19) and mage champion (https://www.dandwiki.com/wiki/Mage_Champion_(5e_Creature)) (CR 23).

Alternatively, you can just use the Warlord statistics and add on spellcasting, as other users have suggested.

Ended up mixing and matching the warlord statistics and abilities with the above linked mage champion. Looks to be a pretty solid enemy.
Huge thanks everyone for the pointers and ideas.

[JNAProductions]

You should share your results!