Walker is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

How it works : Walker

Original English text — Wizards of the Coast / Scryfall

No additional ruling has been published for this card.

Interactions with other cards

These cards' text mentions Walker.

Otawara, Soaring City

{T}: Add {U}. Channel — {3}{U}, Discard this card: Return target artifact, creature, enchantment, or planeswalker to its owner's hand. This ability costs {1} less to activate for each legendary creature you control.

Boros Charm

Choose one — • Boros Charm deals 4 damage to target player or planeswalker. • Permanents you control gain indestructible until end of turn. • Target creature gains double strike until end of turn.

Fell the Profane // Fell Mire

Destroy target creature or planeswalker. As this land enters, you may pay 3 life. If you don't, it enters tapped. {T}: Add {B}.

Mox Amber

{T}: Add one mana of any color among legendary creatures and planeswalkers you control.

Takenuma, Abandoned Mire

{T}: Add {B}. Channel — {3}{B}, Discard this card: Mill three cards, then return a creature or planeswalker card from your graveyard to your hand. This ability costs {1} less to activate for each legendary creature you control.

Braids, Arisen Nightmare

At the beginning of your end step, you may sacrifice an artifact, creature, enchantment, land, or planeswalker. If you do, each opponent may sacrifice a permanent of their choice that shares a card type with it. For each opponent who doesn't, that player loses 2 life and you draw a card.

Spark Double

You may have this creature enter as a copy of a creature or planeswalker you control, except it enters with an additional +1/+1 counter on it if it's a creature, it enters with an additional loyalty counter on it if it's a planeswalker, and it isn't legendary.

Bedevil

Destroy target artifact, creature, or planeswalker.

Adeline, Resplendent Cathar

Vigilance Adeline's power is equal to the number of creatures you control. Whenever you attack, for each opponent, create a 1/1 white Human creature token that's tapped and attacking that player or a planeswalker they control.

The Reaver Cleaver

Equipped creature gets +1/+1 and has trample and "Whenever this creature deals combat damage to a player or planeswalker, create that many Treasure tokens." Equip {3}

Mangara, the Diplomat

Lifelink Whenever an opponent attacks with creatures, if two or more of those creatures are attacking you and/or planeswalkers you control, draw a card. Whenever an opponent casts their second spell each turn, draw a card.