Citadel Siege is a rare Enchantment card from Commander 2016 (C16), collector number 62. Current market price: $0.22, TCGplayer market prices via Scryfall.
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.