17 Clockwork Sorcerer, 1 Hex Blade Warlock, 2 Fighter (Defensive Fighting).
This guy can cast 2 leveled spells in one round using Action Surge. Can use subtle spell to bypass any counterspells. Wins like 75% of initiative rolls due to the spell Alacrity and the feat Awareness. Access to 5e's most powerful cantrip, Eldritch Blast along with Agonizing Blast and only 1 level dip into Hex Blade. Can use medium armor and shield. Knows Wall of Force. Can bind fiends, feys, and elementals. Knows 29 spells, can teleport for free 6 times before rest. Is telepathic. Can change disadvantage/advantaged saves and attacks to either 10 times before rest. Has Armor of Agathys plus Clockwork Warding giving my caster a nice pool of damage reduction and temporary hitpoints. Has the Gate and Wish spell.
Favorite spell combos? Demiplane (wait an hour for the portal door to close) + Gate (call forth your victim sucking them into your Demiplane) + Plane Shift = Bye! Bye! Enjoy eternity in a dark stone room! Sleet Storm with Fireball thrown in. Telekinetic Choke with Quickened Eldritch Blasts
Imagine this guy gets the first drop on a 20th level mage due to the Alert feat + the Alacrity spell. If facing off against another mage my actions would be this:
All in round 1 - Subtle Disintegrate (should be looking rough or dead and can't be countered), Action Surge - Subtle Power Word Stun. All this is overkill but it is a fun show of force. I could also just cast Power Word Stun because most 5e casters have less than 150 hit points or mental prison on a fellow sorcerer (low Int saves). DnD Beyond Build
Or....if you have room, drop a Sleet Storm on them and then a Fireball all in one round using Action Surge. Watch them writhe in your cage of torment. https://www.dndbeyond.com/characters/100258774
Original Clockwork Spell Selection
1st - alarm, protection from evil and good
2nd - aid, lesser restoration
3rd - dispel magic, protection from energy
4th - freedom of movement, summon construct (a spell in chapter 3)
5th - greater restoration, wall of force
My Spell Selection
1st - Feather Fall, Protection from Good and Evil
2nd - Aid, Alter Self
3rd - Dispel Magic, Counterspell
4th - Private Sanctum, Polymorph
5th - Telekinesis, Wall of Force