Da curse of da Monk (5e Optimized Character Build)
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Da curse of da Monk is a rather simple yet elegant build. A simple multi class of monk and wizard centered around my personal favorite spell in the game, bestow curse. One punch is all it takes. Then they shall be stunned for eternity.
Take 6 levels wizard. Choose school of divination. Gain the bestow curse spell and 3 spell slots to cast it with.
Take 14 levels monk. Gain stunning strike.
How it all comes together
It's rather simple. First turn, you cast bestow curse upon an opponent. Use your portent ability to make them fail the saving throw. Choose the effect that gives them disadvantage on certain saving throws. Choose Constitution. Next turn, proceed to rain unarmed strikes galore upon the creature. Each time you hit, try to stun them. They'll have disadvantage on the saving throw and it will be quite unlikely that they'll succeed. When they get stunned, then you'll have advantage on all attack rolls against them and you are almost certainly going to hit at least once per turn. Heck, if you want, take Elven Accuracy (from Xanathar's Guide to everything, not from one of the 3 core books) and always hit your target. You should be able to stun them indefinitely and there's pretty much nothing they can do about it. It can hold down incredibly powerful monsters like Iron Golems or Mummy Lords, and your allies will always have advantage on attacks against them, your wizard friend's spells will always hit, your champion friend will get criticals super often, you're pretty much set! You're only limited by your ki points which will most likely run out well after your enemy's hp will. Weaknesses, you can't use this against swarms. In this case, get some good AOE spells to fight the 2000 kobolds your dm throws against you.
Step By Step Build
This is the way I would play the character. Feel free to mix, match and modify any way you want.
Point Buy with wood elf stats
Str: 8 Dex: 17 Con: 10 Wis: 16 Int: 14 Cha: 8
Monk. Choose Way of the Shadow for general utility and surprise. Might help with landing bestow curse. Use ASI to buff your Dexterity and Wisdom
Wizard. Choose School of Divination. Gain the bestow curse spell and burning hands spells. Maybe a fireball or something. Use ASI to maximize Dexterity.
Monk. Gain as many Ki points as you can. Also diamond soul, pretty broken. Use ASIs to maximize Wisdom and Int. Probably Wis first.