Dragon Traning ProG 10

This is best done with a level 4 dragon. Dragons cannot train at levels 1, 2, or 3, so level 4 is the earliest you can train. The higher the level of your dragon, the more it costs to train them, and the more targets you must hit. At level 4, training costs 200 coins, and has 4 vikings to hit. This means you only need 5000 coins (probably more like 6000 since it's unlikely you'll go 25/25) to unlock the achievement.