In my Mad Mage campaign, I currently have one player playing a dwarf forge cleric / watcher paladin / storm sorcerer. He has full plate that he has enchanted through his forge cleric feature. He also has a shield. And he’s got something else that gives him +2 to AC, so his base AC is 23. Thanks to his sorcerer level, he can also cast shield, making his AC 28 for a round.
He also likes to Dodge to impose disadvantage on enemy attack rolls. Oh, and for the rare occasion where I actually manage to get through all his defenses, he has the Lucky feat and can make me reroll (which more than likely causes me to miss).
He used to rely heavily on dodging plus spirit guardians, but “Halaster” got sick of him doing that, so for a while, every time he cast SG, some mage hunter creatures would appear and attack him. He now doesn’t use SG nearly as much, but he’s still all but impossible to hit.
Dex saves are one of his only weaknesses. (He also has things like the Dungeon Delver feat and a high Perception, so he can automatically find secret doors and resist damage from all the traps.)
He’s as close to being an unkillable “I win!” machine as it’s possible to get in vanilla 5e. One of the most frustrating character combos I’ve ever DMed for! We’re nearly finished the campaign, and I’ve asked the player not to make a character like this again.