What Class or Class combination will raise the largest controlled undead (skeletal) army in 48 hours?

Question

I am planning on making a Necromancer type with the largest undead army available in 5e D&D. He has 48 hours to build it. I have an existing strategy that nets me 150 skeletons using a lv 6 wizard and a lv 14 sorcerer. I would like to hear your ideas.

Rules:

• Hardcover books only, no 3rd party or UA.

• You cannot polymorph into a Beholder... (It breaks the story) You have to be a standard race caster.

• No outside help. You are solo.

• No prep beyond the 48 hours you have to create the army.

• Assume you are at a graveyard with access to enough bodies.

• Lv 20 character, no epic boons unless you have a way to get them through a feat.

• Prefer no magic items, however if you have one that really makes a huge difference let us know.

• We are looking to specifically raise Skeletons. No generals required unless it increases the overall army size.

• All spell slots are available to go towards the army.

• Buffing the army is not necessary, but if you have a way to do it without diminishing its size, I'd love to hear it.

Answer 1

Necromancer Coffeelock

Let's start with the obvious one.

• 9th level Divine Soul sorcerer (5th level spell slot, animate dead, font of magic)
• 11th level Warlock (3 5th level spell slots, recharging on short rest)

Day 1, Midnight Divine Soul casts Animate Dead (1 minute) - giving 5 skeletons, then uses Font of Magic to convert all the Warlock slots to Sorcerer (18 seconds), and casts Animate Dead 3 more times (3 minutes). Then they take a short rest (1 hour).

01:04:18 Wake up, use convert all Warlock slots to Sorcerer (18 seconds), cast Animate Dead 3 more times (3 minutes), then take a short rest (1 hour).

02:07:36 Repeat this 43 more times

Day 2, 23:29:30 no time to rest again, you can relax for the last 30.5 minutes.

Total skeletons: 5 ^{(from the initial sorcerer slot)} + 5 * 3 * 45 ^{(from the warlock slots)} = 680 skeletons

Although note that half of them are not under the control of the character, they are walking around doing their own undead things - probably harassing towns and cities. Be aware that since you have to recast the spell every 24 hours to maintain control, you won't see any benefit to the number of controllable skeletons unless you use your first 24 hours to write scrolls or create rings of spell storage.

If you don't have access to those kinds of items, it may be best to start the attack a day earlier sending skeletons to smaller villages or roads to harass people, then spend the second day building up a main force to attack the city.

EDIT: Actually, I don't think it's necessary to convert the slots to sorcerer, so that should save a lot of seconds.

To be clear - by RAW you can rest whenever you want, the DM doesn't get to choose when the character sits down and relax, and converting non-sorcerer spell slots with flexible casting is RAW.. As always, your DM has the final say on what rules you play at your table. Some DMs have expressed that they wouldn't allow it, but I can't speak for your DM.

Answer 2

Straight level 20 Wizard baseline

A level 20 wizard can control 83 skeletons without using any class features, items, or tricks.

Simply wait until there is 9 hours left on the count down, summon 83 skeletons, then long rest, wake up, summon 83 more.

Total: 83 + 83 = 166

Answer 3

A more legit way of getting actually controlled undead:

20th level necromancy wizard - 158 beefy skeletons

Level 20 wizard with the necromancy specialization is going to be your best way of getting the strongest and most numerous undead horde, without relying on dubious coffeelock cheese that no sane DM will ever allow.

With necromancy specialization, every casting of the spell will allow you to raise (but not remain in control of) one extra corpse.

At this level, you will have 3 3rd, 3 4th, 3 5th 2 6th, 2 7th, 1 8th and 1 9th level spellslot. In addition, you can cast a third level signature spell once per short rest, which we'll also be using to cast Animate Dead.

Arcane Recovery can be used once per day to regain 20 spell levels worth of slots, but only up to 6th level. Best bang for your buck for animating undead is 2 6th, 1 5th and 1 third level spell slot.

Assuming a reasonable DM allows you to short rest twice in a day, together with a good night's rest, you will be casting, in a day: 6 3rd, 3 4th, 4 5th, 4 6th, 2 7th, 1 8th and 1 9th level Animate Dead.

The amount of undead you can raise or control per level: 3rd: Raise 2, maintain control over 4 4th: Raise 4, maintain control over 6 5th: Raise 6, maintain control over 8 6th: Raise 8, maintain control over 10 7th: Raise 10, maintain control over 12 8th: Raise 12, maintain control over 14 9th: Raise 14, maintain control over 16

This means that on your first day, you will raise: 6×2+3×4+4×6+4×8+2×10+12+14 = 126 skeletons.

You've deserved a nap after that, so take a good night's rest. All rested up? Good.

First, we want to make certain we maintain control over all the undead, they are no good to us wandering around aimlessly. 126 skeletons will require us to cast: 3 3rd (12 maintained), 3 4th (18 maintained), 4 5th (32 maintained),4 6th (40 maintained), 2 7th (24 maintained) for a total of 126 skeletons maintained.

We have 3 3rd, 1 8th and 1 9th level spellslot left, which we can use to raise another 32 skeltons, for a grand total of 158 skeletons that are under our control.

You can possibly squeeze out a few more in your 48 hour timespan if you try to abuse the timeframe by raising undead that won't be under your control for much longer, but this is the most straight forward, legit way of without a doubt raising 158 skeletons under your control.

As an added bonus, their hitpoints are 20 higher than a normal skeletons (33 instead of 13), its weapon attacks deal an extra 5 damage (for 1d6+7 in most normal cases). Your skeleton has a 1 in 6 chance of one-shotting a normal skeleton without a critical hit, and even a critical hit from an opponent skeleton has no chance of one-shotting one of your skeletons.

If for some insane reason your DM allows you to long rest more than once per day, or allows infinite short rests like coffeelock assumes, you'll be able to squeeze out extra skeletons, because every extra short rest means another casting of Animate Dead.