Hint: Self-Immolation
When Ash launches a fireball, some flame will linger where you stand. If you morph to a character like Pummel Weed, the flames will alight your character and cause some damage. But you can use Deep Blue with the oil upgrade and shoot napalm.

As Ash, launch a fireball, then quickly morph to Deep Blue and start shooting oil. The oil will be in flames as you shoot it. You will not take damage from the flames because Deep Blue is of the Water element and Fire doesn't affect it.
Hint: Immolation Nation (Ash Life)
Once you unlock Ash's flame circle move, you can use it immolate Ash and recover his life.
Hint: Unlimited Runes (Money)
When you are heading toward the snow temple, you will find this specific spot. When you have to be Major ruin to shooot across a gap and switch to Chilla, you should fall. Below will be an elemental fruit and three ice "balls". Get out Ash and burn them; you should get coins in most of them. Wait until they all rebuild, then do it again; more coins will come out. This process is long, but it works. When your wallet is full, buy the larger size and come back to get more coins. Do this until you have 999 coins. Then you can go to shops and by out all their elemental fruit and whatever else you want.