Clone Army

In 5th edition D&D, it's perfectly within the rules as written to create a Clone Army - an infinite number of simulacra of yourself.

Creating a Clone Army

1. Learn the spells Wish and Simulacrum.
   1. Actually, Wish is optional unless you need speed.
2. Get hold of the materials to cast Simulacrum on yourself once: enough snow or ice to make an identically sized copy of yourself; a strand of your hair, fingernail or similar; and 1500gp worth of powdered ruby.
   1. This step can easily be skipped by using Wish to cast the Simulacrum spell, no material components required or penalties incurred.
      1. Except then your simulacrum needs the components to continue the cycle, since you've already burned your 9th-level slot. If you're in trouble with components or need speed, it's much better to start the cycle with one Simulacrum and then have each simulacrum in the infinite cycle use Wish component-free.
         1. Ignore this objection if you have the Epic Boons of High Magic (a 2nd 9th-level slot) or Spell Recall (the ability to cast a spell once/day without using one of your slots).
   2. Materials can be obtained with the Wish spell since it can spontaneously create items worth up to 25,000 gp - just remember to rest afterwards to regain your use of Wish if you obtain the materials this way.
      1. Never do this: Casting wish for anything except duplicating a spell has a 1/3 chance of burning the ability out of you forever, that's why you have your simulacra cast wish for you. Obtain the ingredients some other way.
3. Create a simulacrum of yourself. This is an exact copy of yourself under your control. It has half of your health, is made from ice and knows every spell that you do - including Wish. It can't regain spell slots so it can only cast Wish once, but that's all you need.
4. One of the uses of Wish is to duplicate the effects of any spell at all of level 8 and below, but with no material requirements and no cast time aside from that required to use Wish - one action. Order your simulacrum to use its Wish to duplicate the effects of Simulacrum with you as its target. This will create another simulacrum of you, which also has the spell Wish learned and available to cast.
   1. Alternatively be a 20th-level caster, so you have 2 7th-level slots, so your simulacrum can cast simulacrum with a 7th-level slot rather than wasting a 9th-level slot. That takes 12 hours and the materials, but if you don't need the clone army quickly and cheaply . . .
   2. Or notice your simulacrum can cast the prepared simulacrum with an 8th-level slot, which lets you either pull this whole chain at 15th level or save a Wish at 17th+ level. Same time/expense issue.
   3. And whatever way you have your first simulacrum do it (Wish, second 7th level slot, 8th-level slot), if you have the time, wait until after a long rest (getting all your slots back) before having your first simulacrum make a simulacrum, so the second and later simulacra of you have all their slots when created.
5. Repeat the above order with your new simulacrum. This will create another simulacrum of you, which again has Wish. Rinse and repeat.
   1. Notice if you did this when you could cast Wish and with one of the not-Wish-using methods of infinities, you now have an infinite number of simulacra who can all cast Wish.

The Clones

Each simulacrum takes 6 seconds to produce (the length of 1 action) and is a perfect clone of you in terms of stats, skills etc. except with half your health. This means they have access to every spell and spell slot that you do at the time of Wish casting. Simulacra can't replenish spell slots, so they can't regain the ninth level slot used to continue the chain of clones and once they have used all of their spell slots they can no longer cast spells. However, since they have access to every spell slot you possess and require just six seconds to replace, any opponent can easily be defeated by an army of high-level casters. Given 24 hours to prepare, you can produce 14,400 clones capable of casting, for example, 14,400 Disintegrates at once for 144000d6+576000 damage in one round. The Tarrasque ain't got shit.