Alchemist
You will unlock Alchemist when you reach level 120. Alchemist is a lot like Exotic Merchant with their upgrades but they are called Experiments in Alchemist and the bonus you get is randomly decided for you. You can run 3 experiments at once, each with their own resources. Dragon Blood, Strange Dust and Exotic Coins. It takes 3 hours to complete an experiment. Since the bonus you get is random, it’s pretty difficult to say when to use each resource. I’ve been using Dragon Blood right from the start. I suggest using Strange Dust whenever your Dragon is 4 stars. Exotic Coins is tricky as there are multiple pages of upgrades inside Exotic Merchant now.
At level 130, you will unlock Transmuting inside Alchemist. Transmuting allows you to convert chests to higher rarity chests. The only good thing here is Epic Chest to Legendary Chest. But it’s very pricey. It costs 500 dragon blood + 1 epic chest to get 1 legendary chest. With 500 dragon blood you can do 10 experiments. So you have to choose if it’s worth it. Remember that at 140, you get Naval Missions. They’ll give you a Legendary Chest each day.
I would say the best way to spend dragon blood is to use them in experiments. When you have collected 1.000 gems, you can spend all remaining dragon blood on transmuting legendary chests, and then you use those 1.000 gems on restocking on Dragon Blood. And repeat this over and over. So collect another 1.000 gems, you might have 1.000 dragon blood left, that’s 2 transmutations, then buy dragon blood again. These values may differ depending on how much you play, so basically how many experiments you do per day.