Cryogenist (5e Subclass)
From D&D Wiki
Frost lingers with every step you take, every breath you make, every spell you cast. You are a master of water and ice; a blizzard waiting to freeze everything to death.
Starting at 1st level, all of your spells that deal damage now deal Cold or Bludgeoning damage (Caster's Choice), unless they already do Cold or Bludgeoning damage, and all slow affects you put on a creature now stack. Also, if you reduce a creatures movement speed to 0 then it becomes Frozen causing it to be stunned until the start of your next turn and getting rid of the slowed effect.
Starting at 6th level, All of your spells that deal Cold damage now slow the target's movement speed by 10 feet for every time it deals damage, ending at the start of your next turn. Also, if the spell that deals cold damage already slows a target then it slows them an additional 5 feet.
Starting at 14th level, You can spend 6 sorcery points to cause all of your spells to shatter frozen and slowed enemies until the start of your next turn. For the duration any time you deal Cold damage to a slowed target you deal double the Cold damage and triple to Frozen targets. When you deal damage in this way and the target is slowed, they are now slowed an additional 10 feet, and if they are Frozen, then you shatter it causing them to no longer be stunned.
Winter is Coming
Starting at 18th level, As an action you can take on the aspect of Winter for one minute, causing all slows you apply to double and all spells affected by Frozen Heart used on Frozen creatures now extend the stun for another round rather than breaking it, and only deal double damage rather than triple. You cannot benefit from this ability again until you finish a long rest.