Okay, so I'm planning out my own set design, it'll be built like a large set somewhat styled off of a core set, although incorporating some newer and original mechanic(s), at least that is the plan. I'm not entirely sure how formatting works for creating original cards on this forum, so for now I'll be using some older methods to just make it clear what a card's abilities are. It'll probably include both original cards and reprints. I'll be aiming for Shandalar as the location for now, but might change my mind later.

I'm calling the set 'False Core' for now, since it's basically like a core set in some ways, and not so much in others, and they've discontinued core sets. I'm aiming for some of the relative simplicity of core sets, but perhaps a slightly higher and tighter power level. Like core sets, I'll be aiming for getting a diversity of simple common effects and abilities for each color into that color's setup. I'll possibly make some tweaks to the way I treat the color pie from standard, at least mechanically speaking, although I'll be trying to stick to the color pie in terms of flavor.

Also unlike core sets, I may not entirely shy away from multi-color cards, especially at rare and uncommon, although I'll avoid having too many of them either.

Each color and color pair will generally have a theme to it, while colorless stuff will serve a purpose of either helping cover up weak points in any color, or just giving someone drafting more stuff they can actually play in their decks without worrying about color, as well as a few utility odds and ends where color shouldn't matter too much, or some common things artifacts tend to be used for.

Also unlike core sets, individual cards may often be slightly more complex than normal, as I'll favor doing things like tagging on minor abilities like scry 1 in order to keep cards worth their converted mana costs over underpowering them.

I'll also be slightly favoring design that would take into account wanting cards to be constructed playable, over limited balance, especially at uncommon or higher rarities, although I'll also try to avoid too many limited bombs as well.

I do want to try to keep the colors balanced against each other as one of the higher priorities though, while still keeping each distinct.

Some themes I'll be going for in each color:

White: White will have a sub-theme related to having and caring about enchantments. They'll also have a bit of a white weenie focus, filling the board with low cmc creatures and/or tokens.
Blue: Blue will have a sub-theme related to having and caring about artifacts. They'll also have a bit of an evasive tempo theme, focusing on various ways to push damage through and slow down the opponent.
Black: Black will have a bit of a sub-theme related to casting sorcery spells, sort of an ideal of raw power drawn up from elaborate rituals that take time and preparation to complete (can't be done at instant speed), and benefiting from this. They'll also have a typical black strategy of paying various things and taking related risks for power and flexibility.
Red: Red will have a bit of a sub-theme related to casting instant spells, sort of an ideal of reacting quickly and surprisingly with wild abandon in reaction to changing battlefield conditions and being constantly ready to push out more power and simple tricks. They'll also have a bit of an 'offense over defense' theme, and a bit of a generic aggro/burn thing going on, trying to overwhelm the opponent by constantly battering down defenses and occasionally smacking to the face.
Green: Green will have a sub-theme related to caring about and casting creature spells, and to a lesser degree about lands. They'll have a bit of ramping going on as well as a focus on large, efficient beaters, or more resilient monsters.

Blue's side-focus on artifacts will be a bit more measured and held back than the other colors' focuses on various card types.

I'm not sure at this point if I want to include planeswalkers, although I'm leaning towards yes, and that they'll be the gatewatch, even if I dislike the retcons and story silliness involved in setting them up, it also helps keep things simple. If I do include planeswalkers, I plan to include some thematic spells for them in their color.

Strategic Preparations
Enchantment {U}
At the start of your upkeep, gain 1 life.
At the start of your upkeep, scry X, where X is the number of other enchantments you control.

Engineer of the Platinum Gear
Creature - Human Artificer {U}
You may look at the top card of your library at any time. You may play the top card of your library as if it were in your hand as long as it is an artifact spell.
: Target artifact you control gains hexproof until the start of your next turn. Untap it.
1/3

Curse of the Last
Sorcery {U}
Destroy target creature.
If that creature is destroyed this turn, and it's toughness is 3 or less, scry 2.

Flare Shot
Instant {U}
Choose one -
* Deal 4 damage to target creature, it can't be regenerated, if that creature would die this turn, exile it instead.
* Deal 2 damage to target player.
* Destroy target non-creature artifact with converted mana cost 2 or less.

Vitality Oak
Creature - Tree Shaman {U}
Whenever you cast your first creature spell of the turn, gain 1 life.
If you control 6 or more lands, Vitality Oak gets +1/+2, reach and vigilance.
When Vitality Oak becomes the target of a spell or ability you don't control, scry 2.
2/3

Herald of the Gleam
Creature - Avatar {R}
Vigilance
Herald of the Gleam's power is equal to the number of enchantments you control.
If you control 5 or more enchantments, Herald of the Gleam has indestructible and hexproof.
Whenever you cast an enchantment spell, scry 1.
*/4

Ritual Keeper
Creature - Skeleton Wizard {R}
Menace
If there are 4 or more sorcery spells in your graveyard, at the start of your first main phase, add to your mana pool.
Ritual Keeper's power is equal to the number of sorcery cards you have in your graveyard.
Whenever you cast a sorcery spell, scry 1.
Discard a Sorcery: Return Ritual Keeper from your graveyard to your hand.
*/2

If you want people to see this, you should post it in the main YMTC board. The community set forum only sees traffic from people already working on a community project. You'd have to draw in any helpers from the main forum. The community sets forum is really just here to keep sets from clogging up the main forum with the amount of posts they generate.

Much of you what you told at the preface was really, really normal stuff: the kind of stuff you would expect almost by default.
However, the first thing I notice from the cards is that all the colors scry now. A lot. And repeatedly. You failed to mention that. They did some of that in Mirrodin and Theros, but I don't think none of them had or stuff that would scry repeatedly off triggers. Also, it's not like people weren't smirking at those "unsummon + scry 1" in theros from design standpoint.

There's also minor formatting errors all over.

Strategic Preparations
"At the beginning of your upkeep, ..."
That "gain 1 life" looks rather laughable next to the second ability as in just how weak it's compared to it.

Engineer of the Platinum Gear
Why does the last ability grant hexproof until "start of your next turn" instead of UEOT?

Curse of the Last
The second ability seems unncessary.
"Destroy target creature. If that creature died this way, ..." (Reign of Terror oracle text)

Flare Shot
Rather messy...

Vitality Oak
This especially feels like the kind of design that is trying to do too much. I would drop one of the three abilities. From the second ability (if kept), I would drop one of the granted keywords or just let it give a p/t boost. A good card to compare this would be Sylvan Advocate. Note how focused that design is even though it's of higher rarity than your card.


Herald of the Gleam
Very messy though at least it has a clear theme. You could drop two of those abilities and make a fine uncommon instead - just saying.
Also "As long as you control five or more enchantments, ..."

Ritual Keeper
Again, a tiresome laundry list of abilities. To me it seems likely that people would forget one or two of those abilities while playing with this.