If "Scrap Worm" attacks while "Ancient Forest" is active, you resolve the turn player’s effect first and then the opponent’s. If both are controlled by the same player, they can be resolved in any order.
If "Scrap Worm" attacks but is flipped face-down by the end of the Battle Phase, its effect does not activate.
If "Book of Moon" is Chained to the effect that destroys "Scrap Worm", it is still destroyed.
The effect to add 1 “Scrap” monster to your hand targets and starts a Chain.
If "Scrap Worm" attacks and "Skill Drain" applied by the time "Scrap Worm’s" effect resolves at the end of the Battle Phase, it is not destroyed.