how would people go on building a shaman build like from the cartoon shaman king
the game will be starting at 1st level and probably going to 20th

Hmm... Maybe path of the ancestral guardian barbarian. Or the Undying or Hexblade patron warlock.

Of course you could probably put a spiritual spin on shadow sorcerer, necromancy or divination wizard, or death or grave clerics.

There is also the order of the profane soul blood hunter, which might fit pretty well.

[Edit]Added hexblade. For some reason when first writing, I didn't think it fit thematically. But certainly does with very little reflavoring.

First thing that comes to mind for me is a Hexblade warlock or the ancestral guardian barbarian depending on how you want to play your character.

I actually have a player who plans on doing something kinda similar with an Elven hexblade who uses a moonblade (starting with only the +1 bonus) then as he connects more with his ancestor(s) the more runes will appear on hit sword granting him more power.

Hexblade.

Your Guardian Ghost is your Patron.