致命的な隙 フェルン is a Weiß Schwarz card from 葬送のフリーレン Vol.2 SFN/S136-081. Compare listings from Singapore Weiß Schwarz sellers on CardJio, then jio them on WhatsApp.
【CONT】 If you have a {copy of this} in your clock, this gets -1 level in hand. 【AUTO】 {CX Combo} [Send the Pants CX (098) from your CX Area to Waiting Room] At the start of your Encore Step, you may pay cost. If you do, choose 1 of the following 2 effects and resolve it, a) "If this is in your front row, deal 2 damage to your opponent, then choose up to 1 {2/0 Event - 095} in your Waiting Room, add it to hand." b) "[(3) Discard 1 card] If this is in your back row, you may pay cost. If you do, look at up to 2 cards from the top of your opponent's deck, choose up to 2 cards from among them, put them on top of your opponent's deck in any order, and send the rest to Waiting Room, then deal 4 damage to your opponent."
This card was printed in Japanese only; the English text above is an unofficial community translation.