Guardian of the Plains
Artifact Enchantment Land Creature – Plains Golem (R)
(Guardian of the Plains isn't a spell, it's affected by summoning sickness, and it has ": Add to your mana pool.")
0/1

Guardian of the Island
Artifact Enchantment Land Creature – Island Golem (R)
(Guardian of the Island isn't a spell, it's affected by summoning sickness, and it has ": Add to your mana pool.")
0/1

Guardian of the Swamp
Artifact Enchantment Land Creature – Swamp Golem (R)
(Guardian of the Swamp isn't a spell, it's affected by summoning sickness, and it has ": Add to your mana pool.")
0/1

Guardian of the Mountain
Artifact Enchantment Land Creature – Mountain Golem (R)
(Guardian of the Mountain isn't a spell, it's affected by summoning sickness, and it has ": Add to your mana pool.")
0/1

Guardian of the Forest
Artifact Enchantment Land Creature – Forest Golem (R)
(Guardian of the Forest isn't a spell, it's affected by summoning sickness, and it has ": Add to your mana pool.")
0/1

YOU READ MY FREAKING MIND. I was going to have Black trigger off of instants and Red trigger off of sorceries, but other than that, this is EXACTLY what I was going to post. Great minds think alike!

GREAT MINDS! WHOOO!

As far as black and red goes, I was really up in the air on it. I ended up going with sorcery in black since discard is one of black's primary mechanics and it is almost always sorcery speed. Honestly though it's probably pretty much interchangeable.

I'm editing my original post to contain the entirey of my entry.
You're welcome

Common Land Cycle
Land

~ enters the battlefield tapped and can't be untapped.
At the beginning of your upkeep step, add C to your mana pool. Until end of turn, this mana doesn't empty from your mana pool as steps and phases end.

OR

Rare Land Cycle
Land

~ enters the battlefield tapped and can't be untapped.
At the beginning of your upkeep step, add C to your mana pool. This mana doesn't empty from your mana pool as steps and phases end.

Gutted Palace
Land (R)
: Add or to your mana pool.
When Gutted Palace enters the battlefield, it doesn't untap during its controller's next untap step.
It stands frozen in time as a mockery of its former self, unchanged but for the steady looting of all its riches.

Haunted Dunes
Land (R)
: Add or to your mana pool.
When Haunted Dunes enters the battlefield, it doesn't untap during its controller's next untap step.
Illpyre's shifting sands unearth ancient graves as often as they create new ones.

Evaporated Reservoir
Land (R)
: Add or to your mana pool.
When Evaporated Reservoir enters the battlefield, it doesn't untap during its controller's next untap step.
What was once a great civilization is now only recognizable by the scar it left on Illpyre.

Effulgent Pond
Land (R)
: Add or to your mana pool.
When Effulgent Pond enters the battlefield, it doesn't untap during its controller's next untap step.
Far beneath the ice, a sickly green light is the only sign that Frostwynd is not dead.

Crowded Sanctuary
Land (R)
: Add or to your mana pool.
When Crowded Sanctuary enters the battlefield, it doesn't untap during its controller's next untap step.
Maraka's habitable climate is as much a curse as a blessing. Refugees flood its borders from both Illpyre and Frostwynd.

Totally ripping off Cato here, but I think that my riff on his idea brings the lands closer together in terms of power. I also thought his lands were too hard to activate. I might have gone too far the other way with these, but I guess I'll let the vote decide that.

Ice Flats
Land
As ~ enters the battlefield, you may reveal 3 cards from your hand that share a card type. If you don't, ~ enters the battlefield tapped.
: Add :W: or :U: to your mana pool.

No need to read 5 cards. The rest of the cycle all works the same way, but for different allied colour combinations.
I wonder if it would be better to match the colours up with deck archetypes instead of mindlessly doing 5 allied colour pairs, but it's hard to say what those archetypes will be at this point. Consider the colour choices up for revision perhaps?

Do you think this could work for the set? Fill the Uncommon hole?

Iron Mine is an enters-battlefield-untapped land with no drawbacks that provides two colors of mana ... *and* has an upside. It's a dual-land-plus (only without basic landtypes). Even if it didn't have the flip ability it'd be too powerful. The Weapon Forge side being a land that has no mana or landfetch ability also violates present land principles.

Even Wizards Weather Tower violates the principle of nothing-strictly-better-than-a-basic. It is a strict upgrade on Island, and it's not even Legendary (the excuse they made to allow Minamo, School at Water's Edge et al was that the then-more-punitive Legend Rule was a substantial enough drawback to make such lands not strictly superior to basics).