MTG Salvation

The Locus one could be anything else but Gates.

Mana Convergence, if I up to pay 2 life to enter untapped, it'll match Tarnished Citadel.

The other idea for Triland Conditional was to have it add mana only if you control a nonland permanent. But then, it's chiken and egg, you need mana to cast a permanent in the first place (except for zero mana artifacts).

Tripain Scry
Land
When Tripain Scry enters the battlefield, you may pay 1. If you do, scry 1.
T, Pay 1 life: Add B, R or U.

Triland conditional
Land
At the beginning of your end step, if you don’t control a multicolored permanent, sacrifice Triland Conditional.
T: Add W, G or R.

Mana Convergence
Land
As Mana Convergence enters the battlefield, you may pay 1 life. If you don’t, it enters the battlefield tapped.
T: Add C.
T, Pay 1 life: Add one mana of any color.

Goldenpost
Land - Locus
Other Locus you control have “T: Add one mana of any color.”
T: Add C.

Lake of Mana
Land
T: Add C.
T: Add one mana of any color. Activate this ability only if you control a colorless nonland permanent.

Rebecca 2.0 1WGB
Legendary Creature - Elf Cleric
Whenever a creature enters the battlefield under your control, you gain 1 life.
Whenever a creature you control dies, attacks or blocks, you gain 1 life.
2/4

The reasor behind Rebecca having 3 triggers is Soul Link. The oracle's text has broken the single trigger in two. It must be because the older text confuses players in case the creature deals and is dealt damage at the same time.

Ancient Reliquary
Land
T: Add one mana of any color. Spend this mana only to cast artifact or enchantment spells.
3, T, Sacrifice Ancient Reliquary: Return target artifact or enchantment card from your graveyard to your hand.

Idyllic Paradise
Land
T: Add C.
T: Add one mana of any color. Activate this ability only if you control four or more lands.

Pool of Dreams
Land
T: Add C.
T: Add one mana of any type that a basic land you control could produce.

Elvish Farmer G
Creature - Elf Druid
T: Add one mana of any color that a basic land you control could produce.
1/1

Northen Druid G
Creature - Human Druid
T: Choose the color of a permanent you control. Add one mana of the chosen color.
1/1

Ajani's Care 1W
Enchantment
Whenever an opponent draws a card, you may gain 1 life.

Priest of the Holy Shield 1WW
Creature - Human Cleric
As long as Priest of the Holy Shield is tapped, it has indestructible.
W, T: Prevent the next 3 damage that would be dealt to target creature.
2/2

Goblin Maniac R
Creature - Goblin
Haste
When Goblin Maniac enters the battlefield, it deals 1 damage to any target.
1/1

Static Shock R
Instant
Static Shock deals 2 damage to any target. If you cast it during your turn, it deals 3 damage to any target instead.

Wizard's Mastery 2UU
Instant
You may tap two untapped wizards you control rather than pay Wizard’s Mastery casting cost.
Counter target spell, activated ability or triggered ability.

Jace's Negación 1UU
Instant
Counter target spell. If you control a legendary permanent, you may draw two cards.

Erratic Illusion 1UU
Creature - Illusion
Flash
When Erratic Illusion enters the battlefield, you may counter target spell.
1/1

Mana Leakage 1UU
Instant
Counter target spell. Spells or activated abilities that would target Mana Leakage cost 2 more to be cast or activated.

Drown in Darkness UB
Instant
Counter target spell unless its controller sacrifices a nonland permanent.

Army of Spirits
Enchantment
Whenever a nontoken creature you control dies, create a black and white 1/1 spirit token with lifelink.

Boros Enchantress 1WR
Creature - Human Druid
Whenever you cast an enchantment spell, Boros Enchantress deals 1 damage to any target and you gain 1 life.
2/2

Hindrance UW
Enchantment
Whenever a creature attacks you or a planeswalker you control, it gets -1/-0 until end of turn.
Whenever a spell or ability of a source you don’t control would target you or a permanent you control, you may gain 1 life.

Life Hunger 1WB
Enchantment
1WB: Sacrifice a creature. Target creature gets +2/+2, deathtouch and lifelink until end of turn.

Rebbeca, Princess of Life 2WG
Legendary Creature - Elf Cleric
Whenever a creature enters the battlefield, you may gain 1 life.
Whenever a creature you control attacks, you may gain 1 life.
Whenever a creature you control blocks, you may gain 1 life.
2/4

Wizard of Silence WWUU
Creature - Human Wizard
Flash
When Wizard of Silence enters the battlefield, you may counter target spell.
When Wizard of Silence enters the battlefield, target player can’t cast spells until end of turn.
2/2

Vigor Cloak WG
Enchantment - Aura
Enchant creature
Enchanted creature has trample.
Whenever you gain life, enchanted creature gets +X/+X until end of turn, where X is the amount of life you gained.

One Land
Land
T: Add one mana of any color. Spend this mana only to cast spells with a converted mana cost of 1 or activate abilities that cost one mana.

I think it's impossible to make a pauper dual that enters untapped. Any condition you add and it either becomes too good or too complex. The workaround is to either make a supportive card or a land tha can produce any color, such as unknown shores.

Watcher of the Gates 1
Artifact Creature - Construct
Vigilance
If a Gate would enter the battlefield under your control and tapped, it enters untapped instead.
1/1

Bicolor only dual A
Land
T: Add W or G. Spend this mana only to cast spells that are white and green or activate abilities of green or white permanents.

I think it's too complex for a common.

Bicolor only dual B
Land
T: Add W or G. Spend this mana only to cast permanent spells or activate abilities of permanents.

Bicolor only dual C
Land
T: Add W or G. Spend this mana only to cast non-permanent spells.

Orzhova Removal: Forgot about fetch lands. So a nonland clause should be added.

Rot: what about upgrading it to "artifact, creature or enchantment" ?

Hmmmmm

Basic Check Land
Land
~ enters the battlefield tapped if you control an untapped mountain or forest. (double negative unless you don't is confusing)
T: Add G or R.

Golgari Tax Collector BBGG
Creature - Human Mercenary
First strike
When Golgari Tax Collector enters the battlefield, you may destroy target nonland permanent.
2/2

Stay Alert WWUU
Instant
Counter target spell. Then create a white 2/2 knight token with vigilance.

Wipe Out 3WB
Sorcery
Destroy all creatures and exile all creatures from all graveyards.

Orzhova Removal BW
Instant
As an additional cost to cast Orzhova Removal, exile a card from your graveyard.
Exile target permanent that shares a type with the card you exiled from your graveyard.

Afterlife Messenger 1WB
Creature - Human cleric
Whenever a creature enters the battlefield under your control, each opponent loses 1 life.
Whenever a creature an opponent control dies, you gain 1 life.
2/2

Angel of Apocalypse 4WWRR
Creature - Angel
Flying
When Angel of Apocalypse enters the battlefield, destroy all other creatures and all artifacts.
5/5

Rot BG
Instant
Destroy target creature with converted mana cost less than or equal to the number of cards in your graveyard.

Half Blood Messenger 3BW
Creature - Angel Vampire
Flying, lifelink
Whenever a creature you don’t control dies, put a +1/+1 counter on Half Blood Messenger.
3/3

Extra Sparks R
Instant
The next time a source you control would deal damage, you may divide that damage as you choose among any number of targets.

Electrosphere 1RR
Enchantment
Whenever you cast an instant or sorcery spell, you may pay 1R. If you do, Electrosphere deals 2 damage to any target.

Flux Reversal 1UU
Instant
Counter target spell. You may untap a permanent.

Poisonous Breath 3BB
Sorcery
Destroy target creature. All other creatures controlled by that player get -1/-1 until end of turn.

Massive Strength 1GG
Instant
Target creature gets +X/+X until end of turn, where X is the number of creatures you control.

Inner Strength 3GG
Instant
Target creature gets +X/+X and trample until end of turn, where X is its converted mana cost.

Force of Green Will 4GGG
Creature - Elemental
When Force of Green Will enters the battlefield, destroy all artifacts and enchantments. Then add GGG.
5/5

Multicolor Cycle
Land
Multicolor Cycle enters the battlefield tapped unless you control a permanent of three or more colors.
T: Add W, R or U.

Maze Land
Land
T: Add C.
T: Add W or U. Activate this ability only if you control a permanent of any color.

Leila, Dark Witch 2 BBRR
Legendary Creature - Human Wizard
Other creatures you control have menace
Whenever a creature you control deals combat damage to an opponent, choose one —
• Target opponent discards a card
• ~ deals 2 damage to any target
3/3

Feels broader, not restricted to races and you got to choose between one effect or the other.

Ghost Shock 2 UB
Instant
Counter target spell, activated or triggered ability unless its controller pays 2 life and discards a card.

Dropped red.

[b]Bola's Cruelty[/b] 1BUR
Instant
Return target nonland permanent to its owner’s hand. Its controller discards 2 cards and Bolas’ Cruelty deals 3 damage to any target.

[b]Underworld Cry[/b] 1BU
Sorcery
Exile all cards from target player’s graveyard. For each card exiled this way, that player puts the top card of their library in their graveyard.

[b]Rakdos' Nuke[/b] 4BR
Sorcery
Destroy all creatures and planeswalkers.
Hellbent — If you have no cards in your hand, each player discards their hand.

[b]Peacewalker[/b] 1W
Creature - Human Advisor
1W, T: Tap target creature. If it’s black or red you gain 2 life.
1/2

[b]Ghost Shock[/b] BRU
Instant
Counter target spell, triggered or activated ability. Ghost Shock deals 2 damage to that spell’s controller and they discard a card.

[b]Frightening Horror[/b] 3BB
Creature - Horror
Flying, menace
When Frightening Horror dies, each opponent loses 5 life.
5/5

[b]Goblet of Life[/b] 4
Artifact
Whenever you cast a spell, you gain 1 life for each card with the same name as that spell in your graveyard.

[b]Rakdos' Spectacle[b] 2BR
Enchantment
Whenever a creature you control deals combat damage to an opponent or planeswalker they control, Rakdos’ Spectacle deals 2 damage to each creature they control unless they discard a card.

[b]Leila, Dark Witch[/b] 1BBRR
Legendary Creature - Human Wizard
Whenever a demon, imp, devil or horror you control deals combat damage to an opponent, that player discards a card and Leila, Dark Witch deals 2 damage to any target.
5/5