haven't featured a five-color Commander deck yet, mainly because I really like focused decks, and the five-color decks often end up as a mishmash of powerful cards and mana fixing. There's nothing wrong with that by any means, but I like building Commander decks around cool interactions and strong themes, so most decks with five-color commanders don't appeal to me quite as much. However, the deck I found for this week (built by hatriarch) might make me eat crow.
This deck uses Reaper King as the commander and isn't scared to include as many ways to trigger him as possible. The first and foremost is the legion of Scarecrows, from the actual One-Eyed Scarecrow to all sorts of Changelings.
Besides the Scarecrow army, the Reaper King has many other methods of triggering. Once you have a single Scarecrow in play, cards like Deadeye Navigator, Flickerwisp, Esperzoa, and Clone all Vindicate your decision to play the deck. Even if all your Scarecrows die, there is no shortage of ways to bring them back from the dead, some of which are reusable every turn (I have a soft spot for Skeleton Shard in particular, as I drafted my deck around it in the first PTQ I won).
It does sound like this costs a ton of mana, but Reaper King has your back. Between Grand Architect, Gilded Lotus, Sol Ring, and a ton of fixers, you should be able to deploy your Scarecrows in a timely fashion. The lands are quite colorful, and if you wanted to put more resources into the deck, Revised dual lands or Ravnica shocklands certainly wouldn't hurt (except for the shocklands, those literally can hurt you).
You could also easily customize this by adding more Scarecrow synergies, either with graveyard recursion effects (Unburial Rites springs to mind) or ways to tutor up specific creatures. I also wouldn't mind a few more card-drawing spells, although the creator of this deck opted for the Howling Mine/Temple Bell route, which may play better in multiplayer.
hatriarch's Reaper King
Commander - Reaper King
Luis Scott-Vargas plays, writes, and makes videos about Magic. He has played on the Pro Tour for almost a decade, and between that and producing content for ChannelFireball, often has his hands full (of cards).