I heard this description of Drona:
He that pleased Lord Shiva using a shower of arrows
Is this true? Please give scriptural references.
Deepest apologies for nonsensical wrong answer before. This information is the closest I could get. Please do not upvote as the correct precise answer would have "a shower of arrows"! However Drona did please Lord Shiva with his archery skills. The legend of Tapkeshwar Mahadev also mentions that both father and son did tapas to Mahadev in this cave, near Dehra Dun.
Again this not the answer containing shower of arrows. However -Drona of the Mahabharata was one of the greatest archers of his era. He was the Guru of both Pandavas and Kauravas. It is believed that Dronacharya did penance for 12 years in a cave near Dehradun in Uttarakhand. The cave is today famous as the Tapkeshwar Temple.
It is said that Shiva appeared before Drona in the cave. He was pleased with the supreme skills of Dronacharya in archery and blessed him.
Several years later, Ashwathama, son of Dronacharya, did penance in the cave standing on one foot. Shiva is believed to have appeared before him and blessed him with great skills in archery.
Today one can see the sculpture of Guru Drona on the entrance of the cave temple.