Join forces -- Starting with you, each player may pay any amount of mana. Each player searches their library for up to X basic land cards, where X is the total amount of mana paid this way, puts them onto the battlefield tapped, then shuffles.
{G}
Eladamri's Vineyard
Enchantment
At the beginning of each player's precombat main phase, that player adds {G}{G}.
{2}{G}
Heartbeat of Spring
Enchantment
Whenever a player taps a land for mana, that player adds one mana of any type that land produced.
{G}
Magus of the Vineyard
Creature - Human Wizard
At the beginning of each player's precombat main phase, that player adds {G}{G}.
1 /
1
{1}{R}{R}
Mana Cache
Enchantment
At the beginning of each player's end step, put a charge counter on Mana Cache for each untapped land that player controls.
Remove a charge counter from Mana Cache: Add {C}. Any player may activate this ability but only during their turn before the end step.
{2}{R}
Mana Flare
Enchantment
Whenever a player taps a land for mana, that player adds one mana of any type that land produced.
{3}
Mana Web
Artifact
Whenever a land an opponent controls is tapped for mana, tap all lands that player controls that could produce any type of mana that land could produce.
{3}{R}
Manabarbs
Enchantment
Whenever a player taps a land for mana, Manabarbs deals 1 damage to that player.
{1}{R}{G}
Overabundance
Enchantment
Whenever a player taps a land for mana, that player adds one mana of any type that land produced, and Overabundance deals 1 damage to the player.
{2}{G}
Rites of Flourishing
Enchantment
At the beginning of each player's draw step, that player draws an additional card.
Each player may play an additional land on each of their turns.
{3}{G}
Vernal Bloom
Enchantment
Whenever a Forest is tapped for mana, its controller adds an additional {G}.
{3}{R}
War's Toll
Enchantment
Whenever an opponent taps a land for mana, tap all lands that player controls.
If a creature an opponent controls attacks, all creatures that opponent controls attack if able.
{3}{R}{G}
Zhur-Taa Ancient
Creature - Beast
Whenever a player taps a land for mana, that player adds one mana of any type that land produced.