Sighted-Caste Sorcerer

Exalted (Whenever a creature you control attacks alone, that creature gets +1/+1 until end of turn.)
{U}: Sighted-Caste Sorcerer gains shroud until end of turn. (It can't be the target of spells or abilities.)

Thijarian Witness

Flash
Bear Witness — Whenever another creature dies, if it was attacking or blocking alone, exile it and investigate. (Create a Clue token. It's an artifact with "{2}, Sacrifice this artifact: Draw a card.")

Frontline Sage

Exalted (Whenever a creature you control attacks alone, that creature gets +1/+1 until end of turn.)
{U}, {T}: Draw a card, then discard a card.

Qasali Pridemage

Exalted (Whenever a creature you control attacks alone, that creature gets +1/+1 until end of turn.)
{1}, Sacrifice Qasali Pridemage: Destroy target artifact or enchantment.

Sigil of Valor

Whenever equipped creature attacks alone, it gets +1/+1 until end of turn for each other creature you control.
Equip {1} ({1}: Attach to target creature you control. Equip only as a sorcery.)

Bilbo's Ring

During your turn, equipped creature has hexproof and can't be blocked.
Whenever equipped creature attacks alone, you draw a card and you lose 1 life.
Equip Halfling {1} ({1}: Attach to target Halfling you control. Equip only as a sorcery.)
Equip {4} ({4}: Attach to target creature you control. Equip only as a sorcery.)

Parallel Thoughts

When Parallel Thoughts enters, search your library for seven cards, exile them in a face-down pile, and shuffle that pile. Then shuffle your library.
If you would draw a card, you may instead put the top card of the pile you exiled into your hand.

Finest Hour

Exalted (Whenever a creature you control attacks alone, that creature gets +1/+1 until end of turn.)
Whenever a creature you control attacks alone, if it's the first combat phase of the turn, untap that creature. After this phase, there is an additional combat phase.

Angelic Benediction

Exalted (Whenever a creature you control attacks alone, that creature gets +1/+1 until end of turn.)
Whenever a creature you control attacks alone, you may tap target creature.

Alhammarret's Archive

If you would gain life, you gain twice that much life instead.
If you would draw a card except the first one you draw in each of your draw steps, draw two cards instead.

Sages of the Anima

If you would draw a card, instead reveal the top three cards of your library. Put all creature cards revealed this way into your hand and the rest on the bottom of your library in any order.

Xenk, Paladin Unbroken

Double strike
Auras you control have exalted. (Whenever a creature you control attacks alone, it gets +1/+1 until end of turn for each instance of exalted among permanents you control.)

Living Conundrum

Hexproof
If you would draw a card while your library has no cards in it, skip that draw instead.
As long as there are no cards in your library, Living Conundrum has base power and toughness 10/10 and has flying and vigilance.

Merchant of Truth

Flying
Whenever a nontoken creature you control dies, investigate.
Clues you control have exalted. (Whenever a creature you control attacks alone, that creature gets +1/+1 until end of turn for each instance of exalted among permanents you control.)

Rafiq of the Many

Exalted (Whenever a creature you control attacks alone, that creature gets +1/+1 until end of turn.)
Whenever a creature you control attacks alone, it gains double strike until end of turn.

Abundance

If you would draw a card, you may instead choose land or nonland and reveal cards from the top of your library until you reveal a card of the chosen kind. Put that card into your hand and put all other cards revealed this way on the bottom of your library in any order.

Solitary Confinement

At the beginning of your upkeep, sacrifice Solitary Confinement unless you discard a card.
Skip your draw step.
You have shroud. (You can't be the target of spells or abilities.)
Prevent all damage that would be dealt to you.

Idolized

Enchant creature
Enchanted creature has "Whenever this creature attacks alone, it gets +X/+X until end of turn, where X is the number of nonland permanents you control."

Archmage Ascension

At the beginning of each end step, if you drew two or more cards this turn, you may put a quest counter on Archmage Ascension.
As long as Archmage Ascension has six or more quest counters on it, if you would draw a card, you may instead search your library for a card, put that card into your hand, then shuffle.

Teferi's Ageless Insight

If you would draw a card except the first one you draw in each of your draw steps, draw two cards instead.

Battlegrace Angel

Flying
Exalted (Whenever a creature you control attacks alone, that creature gets +1/+1 until end of turn.)
Whenever a creature you control attacks alone, it gains lifelink until end of turn.

Giltspire Avenger

Exalted (Whenever a creature you control attacks alone, that creature gets +1/+1 until end of turn.)
{T}: Destroy target creature that dealt damage to you this turn.

Security Bypass

Enchant creature
As long as enchanted creature is attacking alone, it can't be blocked.
Enchanted creature has "Whenever this creature deals combat damage to a player, it connives." (Its controller draws a card, then discards a card. If they discarded a nonland card, they put a +1/+1 counter on this creature.)

Ironsoul Enforcer

Whenever Ironsoul Enforcer or a commander you control attacks alone, return target artifact card from your graveyard to the battlefield.

Tomorrow, Azami's Familiar

If you would draw a card, look at the top three cards of your library instead. Put one of those cards into your hand and the rest on the bottom of your library in any order.

Gutter Shortcut

Enchant creature
Enchanted creature can't be blocked as long as it's attacking alone.
If Gutter Shortcut would be put into a graveyard from anywhere, exile it instead.

Gutter Skulker

Gutter Skulker can't be blocked as long as it's attacking alone.
Disturb {3}{U} (You may cast this card from your graveyard transformed for its disturb cost.)

Gutter Skulker // Gutter Shortcut

Angelic Exaltation

Whenever a creature you control attacks alone, it gets +X/+X until end of turn, where X is the number of creatures you control.

Mr. Foxglove

Lifelink
Whenever Mr. Foxglove attacks, draw cards equal to the number of cards in defending player's hand minus the number of cards in your hand. If you didn't draw cards this way, you may put a creature card from your hand onto the battlefield.

Laboratory Maniac

If you would draw a card while your library has no cards in it, you win the game instead.

Words of Worship

{1}: The next time you would draw a card this turn, you gain 5 life instead.

Arcane Signet

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

Sublime Archangel

Flying
Exalted (Whenever a creature you control attacks alone, that creature gets +1/+1 until end of turn.)
Other creatures you control have exalted. (If a creature has multiple instances of exalted, each triggers separately.)

Ormos, Archive Keeper

Flying
If you would draw a card while your library has no cards in it, instead put five +1/+1 counters on Ormos, Archive Keeper.
{1}{U}{U}, Discard three cards with different names: Draw five cards.

Altar of the Goyf

Whenever a creature you control attacks alone, it gets +X/+X until end of turn, where X is the number of card types among cards in all graveyards.
Lhurgoyf creatures you control have trample.

Noble Hierarch

Exalted (Whenever a creature you control attacks alone, that creature gets +1/+1 until end of turn.)
{T}: Add {G}, {W}, or {U}.

Sovereigns of Lost Alara

Exalted (Whenever a creature you control attacks alone, that creature gets +1/+1 until end of turn.)
Whenever a creature you control attacks alone, you may search your library for an Aura card that could enchant that creature, put it onto the battlefield attached to that creature, then shuffle.