花刀劈怪 The Sword-Dance
小龍接了刀，就留心，在那酒席前上三下四，左五右六，丟開了花刀法。怪看得眼咤。小龍丟了花字，望妖精劈一刀來。好怪物，側身躲過，慌了手腳，舉起一根滿堂紅，架住寶刀。那滿堂紅原是熟鐵打造的，連柄有八九十斤。小龙接了刀，就留心，在那酒席前上三下四，左五右六，丢开了花刀法。怪看得眼咤。小龙丢了花字，望妖精劈一刀来。好怪物，侧身躲过，慌了手脚，举起一根满堂红，架住宝刀。那满堂红原是熟铁打造的，连柄有八九十斤。
逐句解 Line by line
The little dragon took the sword and, on his guard at once, went high and low, left and right before the very feast-table, and set going a flourishing sword-play.
上三下四，左五右六 ("three up, four down, five left, six right") renders his nimble motion; 花刀法 is a showy "flowery sword technique." 那 is deictic nà.
The demon watched, his mouth agape.
看得 takes the structural 得 as de; 眼咤 is to stare open-mouthed in astonishment. The show has entirely captured him.
Then the little dragon dropped the flourishes and slashed a blade straight at the demon.
丟了花字 ("dropped the flowery patterns") — he abandons the display for the real strike, the whole point of the disguise now revealed.
A fine monster! He dodged aside, thrown into a fluster, snatched up one of the "hall-fillers," and blocked the treasured sword with it.
架住 is "to block, to parry." Deprived of his own sword, the demon must fend off the blow with a candelabrum.
That "hall-filler" was forged of wrought iron, and with its shaft weighed eighty or ninety jīn.
熟鐵 is "wrought iron"; 斤 (jīn, a catty, roughly half a kilogram) is left in its romanized form. The improvised weapon is a formidable iron bludgeon. 那 is deictic nà.
The stratagem pays off exactly as designed. The "maid’s" sword-dance, having drawn the demon’s delighted attention, becomes without warning a lethal strike, and the demon — his own blade already surrendered — is reduced to parrying with a candelabrum. The disguise has both armed the dragon and disarmed his foe.
The detail of the wrought-iron "hall-filler," weighing eighty or ninety jīn, converts the ornamental lamp-stand of the feast into a massive bludgeon. The vernacular novel delights in such transformations of the domestic into the martial: the furniture of the revel becomes the weaponry of the fight.