Cheapest priced copy (Throne of Eldraine): $0.49 at Card Kingdom, near mint, their price list as of .
Oathsworn Knight 
Creature — Human Knight · 0/0 · Rare · Throne of Eldraine Promos · #98p
This creature enters with four +1/+1 counters on it.
This creature attacks each combat if able.
If damage would be dealt to this creature while it has a +1/+1 counter on it, prevent that damage and remove a +1/+1 counter from it.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
4 printings · $0.49 to $1.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Throne of Eldraine | 98 | Rare | $0.49 | $0.49 |
| Throne of Eldraine | 354 | Rare | $0.59 | $1.49 |
| Throne of Eldraine Promos | 98p | Rare | $0.49 | $0.99 |
| Throne of Eldraine Promos | 98s | Rare | — | $0.69 |
4 rulings from Wizards of the Coast
- 4 October 2019If damage that can't be prevented is dealt to Oathsworn Knight, one counter is still removed from it.
- 4 October 2019If multiple sources would deal damage to Oathsworn Knight simultaneously (for example, multiple creatures blocking it), its last ability applies once. All of that damage is prevented, and only one counter is removed.
- 4 October 2019If Oathsworn Knight can't attack for any reason (such as being tapped or having come under that player's control that turn), then it doesn't attack. If there's a cost associated with having it attack, its controller isn't forced to pay that cost, so it doesn't have to attack in that case either.
- 4 October 2019Oathsworn Knight's last ability removes only one counter from it each time it would be dealt damage, not one counter per 1 damage prevented.