For an icy character using Armor of Agathys, would a fiend warlock be viable? I figure they'd be in a pact with levistus. Now that any temp HP can keep AoA up with the new wording, having dark ones blessing could be a huge boon, getting back (warlock level)+(CHA mod) whenever an enemy dies within 10 ft of you. Could go pact of the Tome and put repelling blast onto frost bolt to really slow people down. Also, taking the 'Tomb of Levistus' invocation just seems like a really thematic build choice, and with it also using temp HP, would be a great move to use when you know the DM is about to slam you with some beefy, multi attack creature.

Alternatively, would it be better to dip warlock and just go the rest abjuration wizard, for wards and higher level spell slots to cast AoA with, and then polymorph to turn yourself into a giant Ape that pops people for 35 cold damage whenever they touch you? Or maybe a cleric or paladin dip for heavy armor and then heavy armor master feat, so it takes that many more hits to take out the AoA?

Warlock seems the most thematically interesting, but wizard seems to have way more mechanical toys to play with. What do?