Dragon Head Upgrades

Impossible to miss, it's on the other side of the dragon statue as you enter the temple.
As you get to the Toad Weeds outside, turn to the right before the gliding part; there you'll see the Quill on a platform. Use the branch to reach it.
Outside the temple as the spiders first attack. Go to the left and use the tree branches to reach it.
On the highest of five hexagonal pillars in the very next room after the first Health Relic.
Behind some rocks at the top far end of the room with half a broken bridge.

Ancient Grove

Once up the waterfall at the start of the level, go all the way right and you'll find this at the end of a few tree branches.
Inside a large pulsating mushroom directly after the first tree you smash down.
After a lake with rising and falling platforms, smash a tree on the right-hand side of the path and use the branches along the path ahead.

Grove Underground

After the first few lakes you need to cross with ice, stand on a series of small circular platforms to the right, using Dragon Time to reach the top.
In the Jellyfish area after the middle tree. At a fork in the path of Jellyfish go to the right.
After the Jellyfish area smash a tree along the path around the first corner after the Growths.
Inside a box on the deck of a ship half submerged in a purple lake.
On the far side of the above mentioned ship.

Fellmuth Arena

After saving Mole-Yair's people this quill is found by using a cannon in the next open room on the right. Cannonballs are in first open on the left.
Fire a cannon twice in the first room beyond the cannonball room mentioned above.
Fire the left cannon on the deck with two cannons at opposite ends as you first emerge.
At the very top of the first mast you come to, up an extra lift that appears after killing several waves of leaders.
Inside a chest behind the steering wheel at the top of the big fight.

Pirate Fleet

Inside a chest in the first section of the ship you blow a hole in the side of with a cannon.
Underneath the deck of the ship right after the one for Quill 19. Smash the piles of straw at the back of the ship to find a pressure pad to open it. You'll find the quill tucked away behind some crates.
On the ship you smash into with a boat, at the back right side jump onto a few small boats floating out in the sky.
On the ship with three levers, Tail Strike the trap door in the middle several times.
In a treasure chest on the empty ship right after the one with the three levers.

Celestial Caves

In the middle of a frozen pond right surrounded by Stone Trolls.
Use a tilt beam to go to the right instead of in to the left at the previously mentioned frozen pond.
At the next pair of Stone Trolls use a statue with a shield to get up to some branches leading the way to the quill.
Inside the Fire Cave, behind a rock as you enter the cave after the crystal ball spiders.
Left at the doorway after the three crystal ball switches in the Ice Cave.
Turn around at the start of the Earth Cave and jump up the branches.
In the Earth Cave at the point where you free a pair of Button Crabs, use a tilt beam in order to reach this feather.
In the Earth Cave at the part with two crystal ball spiders, push a statue into it's correct position and then use branches to reach this quill on it's little ledge.
Behind some rocks on the far side of the first part of water in the Electric Cave.
To the left of the cave across the second bit of water in the Electric Cave. Push a statue to reach it (unnecessary).

Mountain Fortress

On the second platform from the start, smash some thorns on the way up (not the ones at the very top) to find this hidden feather.
To the right of the green entrance doors at the start of the level.
Above a large green waterfall. From the top glide into it.
In the room with the Yak, Ogre, Troll many waved attack. It's right below the entrance.
In the hallway with a green beam of light right after the above room. It's in plain sight.
After the Assassin fight, jump down to the left.
After the Assassin fight, climb onto the moving platform on the right and at the top glide to where the quill is further out.

1. Temple
Look down into the hole left by a collapsing floor, not long after the first encounter with a Snail Rider.
2. Ancient Grove
At the first tree you knock down in the level, about turn and use the tree branches to reach.
3. Pirate Fleet
Inside a chest in the room after the section with the burning and collapsing floor.
4. Celestial Caves
In the Fire Cave, at the part with platforms and candles, turn around at the top and jump over some books.
5. Mountain Fortress
In the first courtyard with an invisible Commander, smash a thorn bush to the right of the exit, then Tail Strike a button behind it. This opens a door on the opposite side of the courtyard.
Health

1. Temple
After the spider den, turn to the right when standing on a bridge near some Toad Weeds. Glide down to collect.
2. Grove Underground
At the jellyfish section, before going into the middle tree go to the right and follow a series of branches and jellyfish around to this relic. You might need to use Comet Dash to reach all of the branches.
3. Fellmuth Arena
In the place with a series of pressure pads and a rolling barrel, let the barrel get all the way to the end of the path, beyond where it would create an exit.
4. Celestial Caves
In the Ice Cave, directly beneath the first cliff.
5. Mountain Fortress
In the room with the large dragon statue and tons of candles, go up the platforms to the statue then turn around and use a series of rocky platforms stuck to the wall to reach this relic around the other side.