Cheapest priced copy (Forgotten Realms Commander): $0.49 at Card Kingdom, near mint, their price list as of .
Outpost Siege 
Enchantment · Rare · Bloomburrow Commander · #199
As this enchantment enters, choose Khans or Dragons.
• Khans — At the beginning of your upkeep, exile the top card of your library. Until end of turn, you may play that card.
• Dragons — Whenever a creature you control leaves the battlefield, this enchantment deals 1 damage to any target.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
9 printings · $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Forgotten Realms Commander | 135 | Rare | $0.49 | — |
| Bloomburrow Commander | 199 | Rare | $0.49 | — |
| Commander 2017 | 139 | Rare | $0.49 | — |
| Commander 2020 | 157 | Rare | $0.49 | — |
| Commander Legends: Battle for Baldur's Gate | 804 | Rare | $0.49 | — |
| Foundations Commander | 169 | Rare | $0.49 | — |
| Fate Reforged | 110 | Rare | $0.49 | — |
| Fate Reforged | 110★ | Rare | — | — |
| New Capenna Commander | 272 | Rare | $0.49 | — |
6 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 2014The card exiled by the "Khans" ability is exiled face up. Playing a card exiled with the "Khans" ability follows the normal rules for playing the card. You must pay its costs, and you must follow all applicable timing rules. For example, if it's a creature card, you can cast it only during your main phase while the stack is empty.
- 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.
- 24 November 2014Each Siege will have one of the two listed abilities, depending on your choice as it enters the battlefield.
- 24 November 2014If you exile a land card using the "Khans" ability, you may play that land only if you have any available land plays. Normally, this means you can play the land only if you haven't played a land yet that turn.
- 24 November 2014If a noncreature card is manifested and then leaves the battlefield while face down, the "Dragons" ability will trigger.