Negative Nimbus Maze (replacing creature with permanent makes it harder to use)
Land T: Add W. If you control a white creature, add C instead. T: Add U. If you control a blue creature, add C instead.
Conditional Painland (creature instead of any permanent makes it more balanced?)
Land T: Add W. Conditional Painland deals 1 damage to you unless you control a white permanent. T: Add U. Conditional Painland deals 1 damage to you unless you control a blue permanent.
Conditional Tripainland (I think 3 colors among permanents is a bit broader than a multicolored permanent)
Land T: Add W, U or R. Conditional Tripainland deals 2 damage to you unless there are three or more colors among permanents you control.
Super Mountain (cycle)
Land - Mountain
(T: Add R.)
Super Mountain enters the battlefield tapped. T: Add one mana of any color. Activate this ability only if you control two or more red permanents.
Slow Painland
Land
Slow Painland doesn’t untap during your untap step.
At the beginning of your upkeep, you may pay 1 life or 1. If you do, untap Slow Painland. T: Add W or B.
Mishra's Facility (maybe broken?)
Land T: Add CC. Spend this mana only to activate abilities of permanents you control.
Not a Fetch
Land T: Add C. T, Sacrifice Not a Fetch: Reveal the top card of your library. If it’s a land, you may put it onto the battlefield. Otherwise, put it on the bottom of your library.
Engineered Lotus0
Artifact T, Sacrifice Engineered Lotus: Add one mana of any color among permanents you control.
Faraday Cage4
Artifact
Triggered abilities can’t be triggered.
Mishra's Powercore3 (previous incarnation was improvise + very high mana cost)
Artifact
Metalcraft — T: Add CCC. Activate this ability only if you control three or more artifacts.
Silver Lotus3 (the idea is to filter, not to ramp)
Artifact
Silver Lotus enters the battlefield tapped. T, Sacrifice Silver Lotus: Add three mana in any combination of colors.
Vault of the Forgotten4
Artifact
Vault of the Forgotten enters the battlefield tapped. 2, T, Sacrifice Vault of the Forgotten: Exile all nonland colorless permanents.
Cull the Mighty1W
Sorcery
Each player sacrifices the permanent with the highest converted mana cost among permanents they control. If two or more permanents are tied for the cost, its controller chooses one to sacrifice.
Brain Eater1B
Creature - Bird
Flying
When Brain Eater dies, look at target player’s hand. You may choose a nonland card from it. That Player discards that card.
1/2
Putrid Zombie2BB
Creature - Zombie
When Putrid Zombie dies, destroy each creature with converted mana cost four or less and remove one loyalty counter from each planeswalker.
3/3
Wave of Darkness4BB
Sorcery
Choose a color. Destroy all nonartifact creatures that aren’t of the chosen color.
Devourer of the NightBB
Creature - Nightmare Horror
At the beginning of your upkeep, Devourer of the Night deals damage equal to its power to you. 1B: Exile target creature card from a graveyard. Put X +1/+1 counters on Devourer of the Night, where X is that creature’s power.
1/1
Bone Harvester1BB
Creature - Zombie
At the beginning of your upkeep, sacrifice a creature.
Bone Harvester gets +X/+X, where X is the number of creatures in your graveyard.
2/2
Wave of Death3BB
Sorcery
Destroy target creature and all other creatures with the same converted mana cost of that creature.
Last Thought1UU
Instant
Last Thought can’t be countered be spell or abilities.
Counter target spell unless its controller pays 3.
Mind Leak1U
Sorcery
Target player puts the top x cards of their library in their graveyard, where x is the number of permanents they control.
Mana Leakage1UU
Instant
Counter target spell. Spells or activated abilities that would target Mana Leakage cost 2 more to be cast or activated.
Soul Manipulation3UB
Sorcery
Put target creature or planeswalker card from an opponent’s graveyard onto the battlefield under your control.
Not Armageddon1 (very narrow mass land destruction)
Sorcery
Destroy all enchanted lands and all creature lands.
Izzet Leyline2UR (I think this could be a 2/2 wizard)
Enchantment
If Izzet Leyline is in your opening hand, you may begin the game with it on the battlefield.
Instant and sorcery spells can’t be countered.
Hanna's Conviction1WG
Enchantment
Artifact and enchantment spells you cast can’t be countered by spells or abilities.
, Sacrifice Hanna’s Conviction: Destroy target artifact or enchantment and you gain 2 life.
Drown in Blood2UB
Enchantment
At the beginning of your upkeep, target player puts the top three cards of their library into their graveyard. You gain 2 life for each creature card that was put into that graveyard this way.
Survival Instinct
Instant
Target creature gets +1/+2 until end of turn. You gain 2 life and draw a card.
Land
T: Add W. If you control a white creature, add C instead.
T: Add U. If you control a blue creature, add C instead.
Conditional Painland (creature instead of any permanent makes it more balanced?)
Land
T: Add W. Conditional Painland deals 1 damage to you unless you control a white permanent.
T: Add U. Conditional Painland deals 1 damage to you unless you control a blue permanent.
Conditional Tripainland (I think 3 colors among permanents is a bit broader than a multicolored permanent)
Land
T: Add W, U or R. Conditional Tripainland deals 2 damage to you unless there are three or more colors among permanents you control.
Super Mountain (cycle)
Land - Mountain
(T: Add R.)
Super Mountain enters the battlefield tapped.
T: Add one mana of any color. Activate this ability only if you control two or more red permanents.
Slow Painland
Land
Slow Painland doesn’t untap during your untap step.
At the beginning of your upkeep, you may pay 1 life or 1. If you do, untap Slow Painland.
T: Add W or B.
Mishra's Facility (maybe broken?)
Land
T: Add CC. Spend this mana only to activate abilities of permanents you control.
Not a Fetch
Land
T: Add C.
T, Sacrifice Not a Fetch: Reveal the top card of your library. If it’s a land, you may put it onto the battlefield. Otherwise, put it on the bottom of your library.
Engineered Lotus 0
Artifact
T, Sacrifice Engineered Lotus: Add one mana of any color among permanents you control.
Faraday Cage 4
Artifact
Triggered abilities can’t be triggered.
Mishra's Powercore 3 (previous incarnation was improvise + very high mana cost)
Artifact
Metalcraft — T: Add CCC. Activate this ability only if you control three or more artifacts.
Silver Lotus 3 (the idea is to filter, not to ramp)
Artifact
Silver Lotus enters the battlefield tapped.
T, Sacrifice Silver Lotus: Add three mana in any combination of colors.
Vault of the Forgotten 4
Artifact
Vault of the Forgotten enters the battlefield tapped.
2, T, Sacrifice Vault of the Forgotten: Exile all nonland colorless permanents.
Cull the Mighty 1W
Sorcery
Each player sacrifices the permanent with the highest converted mana cost among permanents they control. If two or more permanents are tied for the cost, its controller chooses one to sacrifice.
Brain Eater 1B
Creature - Bird
Flying
When Brain Eater dies, look at target player’s hand. You may choose a nonland card from it. That Player discards that card.
1/2
Putrid Zombie 2BB
Creature - Zombie
When Putrid Zombie dies, destroy each creature with converted mana cost four or less and remove one loyalty counter from each planeswalker.
3/3
Wave of Darkness 4BB
Sorcery
Choose a color. Destroy all nonartifact creatures that aren’t of the chosen color.
Devourer of the Night BB
Creature - Nightmare Horror
At the beginning of your upkeep, Devourer of the Night deals damage equal to its power to you.
1B: Exile target creature card from a graveyard. Put X +1/+1 counters on Devourer of the Night, where X is that creature’s power.
1/1
Bone Harvester 1BB
Creature - Zombie
At the beginning of your upkeep, sacrifice a creature.
Bone Harvester gets +X/+X, where X is the number of creatures in your graveyard.
2/2
Wave of Death 3BB
Sorcery
Destroy target creature and all other creatures with the same converted mana cost of that creature.
Last Thought 1UU
Instant
Last Thought can’t be countered be spell or abilities.
Counter target spell unless its controller pays 3.
Mind Leak 1U
Sorcery
Target player puts the top x cards of their library in their graveyard, where x is the number of permanents they control.
Mana Leakage 1UU
Instant
Counter target spell. Spells or activated abilities that would target Mana Leakage cost 2 more to be cast or activated.
Soul Manipulation 3UB
Sorcery
Put target creature or planeswalker card from an opponent’s graveyard onto the battlefield under your control.
Not Armageddon 1 (very narrow mass land destruction)
Sorcery
Destroy all enchanted lands and all creature lands.
Izzet Leyline 2UR (I think this could be a 2/2 wizard)
Enchantment
If Izzet Leyline is in your opening hand, you may begin the game with it on the battlefield.
Instant and sorcery spells can’t be countered.
Hanna's Conviction 1WG
Enchantment
Artifact and enchantment spells you cast can’t be countered by spells or abilities.
, Sacrifice Hanna’s Conviction: Destroy target artifact or enchantment and you gain 2 life.
Drown in Blood 2UB
Enchantment
At the beginning of your upkeep, target player puts the top three cards of their library into their graveyard. You gain 2 life for each creature card that was put into that graveyard this way.
Survival Instinct
Instant
Target creature gets +1/+2 until end of turn. You gain 2 life and draw a card.