The text doesn't actually say "opponent's" attacking monster in game. It just says 1 attacking monster. This card SHOULD let you use it on your own monsters but it doesn't work. Either the game needs to fix the text or fix the card.
It's a trap card. Why would it be anything other than an opponent attack?
What the heck...if you chain two enchanted javelins together you get a net LP gain. I started at 4000 LP was attacked by 2400 atk monster. Two enchanted javelins later and my LP is 6400. Is this a bug?