Hitchhiker's Guide to The Undertale Omniverse

Alright, this might be a confusing one folks.
I'm going to try and explain how canon works in this fandom, along with Alternate Universes in General. Strap yourselves in everyone, this'll take awhile. This is going to be based on Community Output, so give any criticism you want.
First of all, Lets explain what Undertale AUs are.
So, There's The Original Game Undertale, an Indie Single-Player RPG Roleplaying Game. There are alternate universes of it which change something. Change the characters, the setting, remove some characters, add some, and so on, and so forth.
If you need to know more, see Underfell or Underswap
Alright, now to explain each canon tier and what fits into them.
== Tier 1 - Toby Fox Canon ==
This is all stuff that is completely 100% Canon to Undertale itself. The Only Canon Material here is Undertale itself, along with Deltarune. This considers all AUs outside of Deltarune Non-Canon. This is The Canon you're going by if you don't want to enter into the community. If you want to know more, see Undertale and Deltarune.
== Tier 2 - Timeline Canon ==
This is things that are only canon to their own multiverses, and widely accepted throughout the community. This canon has a certain set of AUs which are considered to be canon. It adds onto The Toby Fox Canon and expands on it. It gets a bit crazy, but not to much yet. This is the canon you'll use for most stories, because it's one of the easier canons to abide by.
- Most AUs which have nothing to do with alternate timelines are canon. Such as Underfell, Underswap, Storyshift, etc.
- Error and Ink are part of this canon, as The Embodiments of Creation and Destruction. They are the only real "Gods" of this universe, with Dream and Nightmare being moreso Demigods if anything.
- X-Tale is also apart of this canon to some extent. The X-Event is only canon in the confines of Underverse's Canon, which is an altered version of this Canon, but X-Tale's events all happened the same here, barring The X-Event.
- Dreamtale is Canon.
If you need to know more, see Underverse
== Tier 3 - Alternate Canons ==
These consider more than one multiverse exist, and consider most multiverses are canon. There are many, but the most known is Dreamswap. This starts the confusion and dive into the rabbit hole. 
If you need to know more, see Dreamswap
== Tier 4 - Alphaverse Canon ==
Here, this considers Alphatale and all of its corresponding AUs to be canon to The Original Multiverse. Making Error and Ink mere puppets to King Multiverse and Error404. This alters many things, however The Alphatale page tells you basically nothing, you'll have to look up Alphatale elsewhere instead. If you're confused about Ink and Error being puppets, see Error404 and King Multiverse
== Tier 5 - Infinitey Code Canon ==
Alright, we're really spiraling into Insanity now. Infinitey Code's Canon is based on The character himself, and all the characters associated with it. In reality here, this is essentially just an upgrade of The Alphaverse Canon. There's not much originality, and instead, it's simply an Evil God Conquering everything. It's not really that interesting in my eyes.
If you need to know more, see Infinitey Code (The Ultimate Enemy of the Undertale Fandom)
== Tier 6 - Fanon ==
Alright.
This Tier has no coherency, and forces you to take every single bit of information about Undertale and it's AUs as canon. Barring some things. 4th Breaker is now canon, despite the gaps that creates, everything fucking exists here. It's actual hell at this point. I don't know how this was made. Please fucking save me now.
If you need to know more, see 4th Breaker Z-Sans
== Tier 7 - The Infinity Spaghetti Man Canon. ==
This is Even worse.
It considers ALL JOKE CHARACTERS CANON.
LITERALLY EVERYTHING IS FUCKING CANON HERE.
Never go to these depths. None have returned from this hellscape. 
If you delve this far, brace yourself...
If you need to know more, see The Infinity Spaghetti Man's Rampage