Cheapest priced copy (Commander 2016): $0.49 at Card Kingdom, near mint, their price list as of .
Citadel Siege 
Enchantment · Rare · Fate Reforged · #8
As this enchantment enters, choose Khans or Dragons.
• Khans — At the beginning of combat on your turn, put two +1/+1 counters on target creature you control.
• Dragons — At the beginning of combat on each opponent's turn, tap target creature that player controls.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
6 printings · $0.49 to $0.69 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander 2016 | 62 | Rare | $0.49 | — |
| Commander 2021 | 85 | Rare | $0.49 | — |
| Commander Anthology Volume II | 21 | Rare | $0.69 | — |
| Fate Reforged | 8 | Rare | $0.49 | — |
| Fate Reforged | 8★ | Rare | — | — |
| Midnight Hunt Commander | 81 | Rare | $0.49 | — |
3 rulings from Wizards of the Coast
- 24 November 2014Each of the last two abilities is linked to the first ability. They each refer only to the choice made as a result of the first ability. If a permanent enters the battlefield as a copy of one of the Sieges, its controller will make a new choice for that Siege. Which ability the copy has won't depend on the choice made for the original permanent.
- 24 November 2014Each Siege will have one of the two listed abilities, depending on your choice as it enters the battlefield.
- 24 November 2014The words “Khans” and “Dragons” are anchor words, connecting your choice to the appropriate ability. Anchor words are a new rules concept. “[Anchor word] — [Ability]” means “As long as you chose [anchor word] as this permanent entered the battlefield, this permanent has [ability].” Notably, the anchor word “Dragons” has no connection to the creature type Dragon.