Cheapest priced copy (Lorwyn Eclipsed Commander): $2.99 at Card Kingdom, near mint, their price list as of .
Realmwalker 
Creature — Shapeshifter · 2/3 · Rare · Kaldheim · #366
Changeling (This card is every creature type.)
As this creature enters, choose a creature type.
You may look at the top card of your library any time.
You may cast creature spells of the chosen type from the top of your library.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
10 printings · $2.99 to $27.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander Masters | 909 | Rare | $3.49 | — |
| Lorwyn Eclipsed Commander | 114 | Rare | $2.99 | — |
| Kaldheim | 188 | Rare | $2.99 | $4.49 |
| Kaldheim | 366 | Rare | $4.49 | $6.99 |
| Kaldheim | 399 | Rare | — | $5.99 |
| The Lost Caverns of Ixalan Commander | 250 | Rare | $2.99 | — |
| Kaldheim Promos | 188p | Rare | $4.49 | $5.99 |
| Kaldheim Promos | 188s | Rare | — | $7.49 |
| The List | KHM-188 | Rare | $3.99 | — |
| Secret Lair Drop | 1724 | Rare | $20.99 | $27.99 |
7 rulings from Wizards of the Coast
- 5 February 2021If the top card of your library changes while you're casting a spell, playing a land, or activating an ability, you can't look at the new top card until you finish doing so. This means that if you cast a spell from the top of your library, you can't look at the next one until you're done paying for that spell.
- 5 February 2021You can look at the top card of your library whenever you want (with one restriction; see below), even if you don't have priority. This action doesn't use the stack. Knowing what that card is becomes part of the information you have access to, just like you can look at the cards in your hand.
- 5 February 2021You must choose an existing creature type, such as Elk or Advisor. You can't choose card types (e.g., artifact) or supertypes (e.g., snow).
- 5 February 2021Realmwalker doesn't change when you can cast creature spells. Normally, this means during your main phase when the stack is empty, although flash may change this.
- 5 February 2021If Realmwalker is somehow on the battlefield with no choice having been made for it, you may still look at the top card of your library any time. You won't be able to cast any creature spells from the top of your library, even if they have no creature types.
- 5 February 2021The top card of your library isn't in your hand, so you can't foretell it, discard it, or activate any of its activated abilities.
- 5 February 2021You'll still pay all costs for the spell, including additional costs. You may also pay alternative costs if any are available.