Plains

Sacred Foundry

({T}: Add {R} or {W}.)
As Sacred Foundry enters, you may pay 2 life. If you don't, it enters tapped.

Hallowed Fountain

({T}: Add {W} or {U}.)
As Hallowed Fountain enters, you may pay 2 life. If you don't, it enters tapped.

Lavaglide Pathway

Riverglide Pathway

Riverglide Pathway // Lavaglide Pathway

Narset, Enlightened Master

First strike, hexproof
Whenever Narset, Enlightened Master attacks, exile the top four cards of your library. Until end of turn, you may cast noncreature spells from among those cards without paying their mana costs.

Boros Signet

Inspired Ultimatum

Target player gains 5 life, Inspired Ultimatum deals 5 damage to any target, then you draw five cards.

Spectator Seating

Spectator Seating enters tapped unless you have two or more opponents.
{T}: Add {R} or {W}.

Steam Vents

({T}: Add {U} or {R}.)
As Steam Vents enters, you may pay 2 life. If you don't, it enters tapped.

Command Tower

{T}: Add one mana of any color in your commander's color identity.

Sea of Clouds

Sea of Clouds enters tapped unless you have two or more opponents.
{T}: Add {W} or {U}.

Sol Ring

Pillarverge Pathway

Needleverge Pathway

Needleverge Pathway // Pillarverge Pathway

Mystic Monastery

Mystic Monastery enters tapped.
{T}: Add {U}, {R}, or {W}.

Mountain

Reliquary Tower

You have no maximum hand size.
{T}: Add {C}.

Mistgate Pathway

Hengegate Pathway

Hengegate Pathway // Mistgate Pathway

Azorius Signet

Training Center

Training Center enters tapped unless you have two or more opponents.
{T}: Add {U} or {R}.