Arcane Mastery

I strongly reject level requirements on feats; it's too easy to make them a crutch for poor design. The first two bullets (Arcana Expertise/ Half-feat) are already a bit ahead of the curve if you compare them to the Prodigy Feat from Xanathar's Guide. I have no idea what 

• You can turn 3 third level spell into a Cantrip

Is supposed to mean. You can do so without expending a spell slot? Is that the wizard capstone feature Signature Spells as a feat? Even if you limit it to 20, I can't see the reasoning behind letting a level 20 sorcerer learn every targetted spell in the game AND get the wizard 20th level feature with just a feat.

Thank you for your reply and I will hope to answer what I am able to.  Might as well start with your first issue about the level requirement.

1:  The reason I had put a level requirement was for because of the feat was because of the the ability to turn one 3rd level spell into a cantrip. That was my reasoning, but I do understand why people do not like having a level requirement on feats in fact i am one of those people. I probably could of made the 3rd level spell an unlock able ability when reaching 18 level like I did with the ability to adsorb spells at 20th level. Something like that?

2: The second issue. The ability to turn one 3 third level spell into a cantrip. I actually got the idea from a homebrew item called an "Arcane Eye" it is a ring that when attuned to the player has the ability to turn one spell ranging from 1st level to 5th level into a cantrip. and that is kind of it.  It really does not have anything to do with "Signature Spells" it was kind of a quiescence.

By the way I could not find anything about (Arcana Expertise) and I have never played with (Half-feats) so I can not mention anything about that with out any form reliability.  Finally I am not very sure why bring up the feat Prodigy.

Thank you very much for commenting on my Feat I could of been more clear about somethings and it is very possible to change the leveling requirement around.

To clarify some terms; "Expertise" is shorthand for a feature that doubles your proficiency bonus for ability checks on a specific skill, "Half-Feat" describes feats that include a +1 to an ability score. These terms aren't official, just a way of categorizing common trends in feature writing. The sum of this is that your feat shares some traits with Prodigy. The Prodigy feat also doubles the user's proficiency bonus on an ability check with a skill. If you selected the Arcana skill for that benefit, you'd have the same effect without the ability score bonus.

"Turn a 3rd level spell into a cantrip" is a short phrase that implies a much more complicated set of rules: Effective spell level for interactions with counterspell and dispel magic, bonus action spellcasting limitations, and any number of class features which trigger conditional on the level of a spell cast. I'm not sure to what extent you intend any of these interactions so my hope was that you only meant to imply the spell was cast without expending a spell slot. To that end I looked at the high-level wizard class features for language.

The wizard feature Signature Spells:

When you reach 20th level, you gain mastery over two powerful spells and can cast them with little effort. Choose two 3rd-level wizard spells in your spellbook as your signature spells. You always have these spells prepared, they don’t count against the number of spells you have prepared, and you can cast each of them once at 3rd level without expending a spell slot. When you do so, you can’t do so again until you finish a short or long rest.

I'll grant it's more like the 18th level wizard feature Spell Mastery:

At 18th level, you have achieved such mastery over certain spells that you can cast them at will. Choose a 1st-level wizard spell and a 2nd-level wizard spell that are in your spellbook. You can cast those spells at their lowest level without expending a spell slot when you have them prepared. If you want to cast either spell at a higher level, you must expend a spell slot as normal.

Between the two, we see the use of unlimited spellcasting cuts off at 2nd level spells. Even as a 20th level feature, wizards can't cast 3rd level spells without limit. So

1. I don't think the feature is appropriate on a feat
2. If you're going to disregard 1, you need to enumerate the mechanical consequences of what you're trying to do. 

Oh yes I do understand your concerns and do appreciate your suggestions. I also have a version 2.0 in the works.  Yet I do believe I need to talk about the campaigns I participate in.  The group I play with are all "Power Gamer" (mainly because our Dungeon Masters are a bunch of satists lol) and it is not uncommon to be facing  low tier mid-bosses  with well over 1000 HP with minions, when are level 4-6. It is granted that this feat is a little bit over powered most games.  but it is a feat that has been tested many times by multiple people in my group in different games. But trust me we have fighters at level 100 who have taken tough for every feat and still can die to a single Kobold in one hit.  I relies now that most homebrew games are probably not like this.

I also realized i had messed up it was only exposed to be one third level spell not three that was my mistake and i had fixed it on version 2

This god level, magical megaman feat is overpowered,, even for late game.  Take two of the options listed.