MTGNexus

Krzno Observatory
Legendary Land
As Krzno Observatory enters, choose any number of players. Each chosen player reveals the top card of their library. Note the colors of each card revealed this way.
T: Add one mana of a color noted by Krzno Observatory.
.
Defne's Observatory
Legendary Land
When Defne's Observatory enters, target player reveals their hand. Note each color of a card revealed this way.
T: Add one mana of a color noted by Defne's Observatory.

Misty Mausoleum
Land
Champion a creature
T: Add one mana of the creature championed by Misty Mausoleum.
4: Misty Mausoleum becomes a copy of the creature it championed until end of turn.

Torch the Library -- XBB
Sorcery {U}
Search target player's library for a card with each mana value from 0 to X and exile them. (If X is 3, search that player's library for a card with mana value 0, another with mana value 1, and so on up to 3.) Then that player shuffles.

Alleycat Squabble -- 3B
Sorcery {R}
Target opponent puts a card from their hand onto the battlefield as a black Cat creature with base power and toughness each equal to that card's mana value. Then you choose a card in your hand and put it onto the battlefield as a black Cat creature with base power and toughness each equal to that card's mana value. Then those two creatures fight.
Repeat this process until one player does not have any cards in hand, then return all Cats that entered this way to their owner's hand.

Reach for the Horizon -- UG
Sorcery {U}
Search your library for a land card and put it onto the battlefield with a phasing counter on it, then shuffle.

Lush Meadows
Land {U}
When Lush Meadows enters, put a harvest counter on target land.
T: Add G.
1, T: Add G for each land you control with a harvest counter on it.

Lush Shoreline
Land {U}
When Lush Shorelineenters, put a harvest counter on target land.
T: Add G.
1, T: Add G for each land you control with a harvest counter on it.

Lush Moorland
Land {U}
When Lush Moorlands enters, put a harvest counter on target land.
T: Add G.
1, T: Add G for each land you control with a harvest counter on it.

Lush Mountainside
Land {U}
When Lush Mountainside enters, put a harvest counter on target land.
T: Add G.
1, T: Add G for each land you control with a harvest counter on it.

Lush Woodlands
Land {U}
When Lush Woodlands enters, put a harvest counter on target land.
T: Add G.
1, T: Add G for each land you control with a harvest counter on it.

Yes, it's intentional to grow with multiples, although I feel that since it doesn't really kick in until you get to three or four in play (spend 3 to add nine G!) it's probably balanced. If the second ability goes up to costing 2 to activate, it's worthless with only one on the battlefield, provides color filtering with two in play, and only becomes mana positive at 3+.

Oracle of Bren Grotto -- 1UG
Creature - Human Seer {U}
Each other player plays with the top card of their library revealed.
For each creature card revealed this way, Oracle of Bren Grotto gets +1/+1.
For each land card revealed this way, Oracle of Bren Grotto gains ward 1.
2UUGG, T: You may cast an instant or sorcery card revealed this way without paying its mana cost.
2/2

Fedic of the Swordstroke -- WBR
Legendary Creature - Human Soldier {R}
First strike, vigilance
Whenever another creature you control blocks, if it has an ability that would trigger when it attacks, that ability triggers as though it had attacked.
3/1

Ghastly Crew -- B
Enchantment
You may discard creature cards to pay the crew costs of Vehicles you control. (A crew 2 cost may be paid by discarding creature cards with a total combined power of 2 or more.)
Whenever a Vehicle you control deals combat damage to an opponent, you may pay BB. If you do, create a 2/2 black Spirit creature.

Since, sigh, Skeleton Crew is already taken.

Unending Echo -- U
Enchantment
At the beginning of your upkeep, you may pay echo and cumulative upkeep costs of permanents you control an additional time.

Braid of Fire tech?

Kyalla, Deft Duelist - 1WW
Legendary Creature - Human Soldier {R}
If a +1/+1 counter would be put on a creature you control, you may put a shield counter on that creature instead.
2/3

Suck the Spark -- 1BBW
Sorcery {R}
Destroy target Planeswalker. You may put a number of loyalty counters equal to the highest cost amongst loyalty abilities it had onto a Planeswalker you control.
"Yeah, your soul sucks, too!'

Adaptive Armaments -- 2U
Artifact - Equipment
When Adaptive Armaments enters, create a Sword token. (It's an Equipment artifact with "Equipped creature gets +1/+0" and "Equip 0.")
Whenever equipped creature attacks, you may have Adaptive Armaments become a copy of target Equipment until end of combat.
Equip 2U

Terrormorph - 2RRGG
Creature - Elemental. {R}
Imprint - When Terrormorph enters, you may search your library for up to three land cards, exile them, and shuffle. If you do, put two +1/+1 counters on Terrormorph for each land card exiled this way.
T: For each land card imprinted on Terrormorph, add one mana of a color that land could produce.
6/6

Yes, imprint has always been an artifact ability, but it works well here.

Also, there have been plenty of arguments back and forth about how significant filtering land out of your deck is. This isn't quite Mana Severance, but 3 cards might prove it's worth it.

Gialla, Morning's Glare -- 2WWWW
Legendary Creature - Avatar {R}
Lifelink
Whenever Gialla, Morning's Glare deals combat damage to a player, until the end of turn, if that player would add mana, that player adds that much W instead.
6/6

Thunderstorm Peak
Legendary Land {R}
T: Add C
T:: Add RRR. Spend this mana only to cast a spell named Burst Lightning, Chain Lightning, Electrostatic Bolt, Forked Bolt, Lightning Bolt, Shower of Sparks, Spark Jolt, or Storm Strike.

Gialla's Luminous Throne -- WWW
Legendary Artifact {R}
Whenever you cast a spell, gain life equal to the number of white mana symbols in its mana cost.

Lack-lustre Ooze -- BBB
Creature - Ooze {U}
Lack-Lustre Ooze enters with two +1/+1 counters on it.
At the beginning of your upkeep, choose a counter on target creature. That counter becomes a -1/-1 counter.
3/3

Vinecutter Elf -- G
Creature - Elf Druid {C}
Vigilance
T: Add C. If Vinecutter Elf attacked this turn, you may add G instead. If Vinecutter Elf dealt combat damage this turn, you may add GG instead.
0/2

Rhanaja Dhum, Fist of Mercy - RR(R/W)WW
Legendary Creature - Human Monk. {M}
First strike, vigilance
R(r/w)W: Rhanaja Dhum gains doublestrike until end of turn. Your opponents can't lose the game this turn.
3/4

Trying to see how this might play out in terms of multiplayer politics.

Launch into the Aethersphere -- UW
Enchantment - Aura {U}
Enchant creature
At the beginning of your end step, put a flying counter on enchanted creature.
When the number of flying counters on enchanted permanent exceed its mana value, exile it.

Dull Future -- UB
Instant
Tap target creature. Put a stun counter on it and a finality counter.

Crazy Hijinks -- U(U/R)R
Instant {U}
Switch target creature's power and toughness until end of turn. It deals damage equal to its (new) power to any target.

Surficiency -- UG
Instant {U}
Whenever a player adds mana from a land source this turn, that player adds that much C instead.
Whenever a player adds mana from a non-land source this turn, that player adds that much mana of a color of their source instead.

Offer It Up -- CCU
Instant {U}
Each other player draws two cards and reveals their hand. They can't cast spells this turn.
Draw a card.