Using B (xbox) or O (ps4) to kill it.
Killing behemoth from timed quest 5 hunt 4 in about 2 minutes, not counting time to position. Make sure you're at least as high as I am when hitting him or he'll knock you back 30 feet and you'll have to start over.
Credit    • 【ＦＦＸＶ】LV.140極惡兇惡巨獸之王（超犯規的方法輕鬆打）