Pixel Dungeon

Grass breaks line of sight. (Not when you stand in it, but when it's between you and an enemy)
A single tuft of grass allows you to infinitely surprise attack an enemy if you just run in a ◇ around it, attacking every other turn. (Same a single stone pillar) Fishing with the huntress is trivial which saves you an invisibility potion and gives you the fishes' meat for food.

I personally don't like the sniper much, but love the warden. The skill that gives you barksin when trampling grass boosts your armor a lot.
The skill that regrows grass every x turns makes the barksin almost always up, not to menton the extra dew and seeds.

I think especially with the huntress, kiting and positioning is important.
You can break away from an enemy as long as you have a single square of grass or stone. Like with the surprise attacks by going around it in a ◇ pattern.. just move twice without attacking them and then away.
Helpful against skeletons, not so much against crabs.

You can cook spent darts in the alchemy pot with seeds to recreate whatever effect, not that I use darts much.

Using a (+) rune on the bow is nice because the bow's upgrades can't delete those.

For mage... you can go battlemage and put the scrolls of upgrade into the staff... easier, since I do not have to hoard my scrolls until the end of the game.

This is not unique to Battlemage. Not sure what gave you that impression. You should put your first few scrolls into the staff even if you plan to be a Warlock. Hell, I usually put my first 7 scrolls into the mage's staff to make it have 10 zaps (staff of magic missile has 3 zaps at +0 instead of the usual 2, so at +7 it has 10 zaps).

If an enemy is right next to you, and you step away from them into tall grass, and then you step away from them again, your next melee attack will be a surprise attack and won't miss. This is because—for a split second—they couldn't see you while there was tall grass in between you. This is because you move first, then they move. It happens very fast, but for a time, the tall grass was between you.

In addition, I'd you don't attack them, and instead step away from them into another patch of tall grass, they will get confused (and show a "?" above their head) and now they have given up on chasing you and will move in a random direction.

Only the Huntress can do this because every other class will trample the grass.

If you find a ring of sharpshooting I'd pump some scrolls into that instead of into the weapon. Makes the bow OP. Projection enchantment is also great to snipe enemies through walls.

The Huntress starts with a useful Spirit Bow, but her starting melee weapon, the Studded Gloves, is extremely weak. This is an extremely serious weakness of the Huntress in the early game, but can be overcome by replacing the gloves with a better melee weapon (try to replace the gloves as soon as possible).

She can go through tall grass without trampling it, making it easier to surprise attack the enemies. Besides, with her Rejuvenating Steps talent, she can also create grass and have additional dewdrops and seeds. And with her Heightened Senses, the Huntress can detect enemies behind doors or walls (sometimes it helps her detect secret rooms). When combining Rejuvenating Steps and Heightened Senses (and a Wand of Fireblast or Disintegration), she can replace doors with grass and easily defeating DM-200s and Golems (as in the attached file).

With her Spirit Bow, the Huntress can attack enemies afar without worrying about thrown weapons breaking or running out (Darts can't be broken but they can run out). Her bow can also be enchanted, giving extra abilities (with a Crossbow, Darts can be (indirectly) enchanted, but, again, they can run out). (With her bow, I think Darts are unnecessary, you can save money for other things). The bow upgrades itself after every five levels of the Huntress, so you don't need to spend precious Scrolls of Upgrade on the bow, you can spend them on weapons and armors instead.

...

(The Huntress is actually my favourite hero).

The distinct advantage huntress has is the bow, which let's you whittle down the hp of enemies before you go into hand to hand combat. It is also important to note that your bow can be enchanted, which it is a good idea to do as soon as you find a stone of enchantment, since you use the bow the entire run.

You can apply the warrior dump-all-scrolls-on-scale-armor on every single run, with every single character, and then the game becomes just easy. Except on Faith Is My Armor, you can't there.

Not trampling grass is extremely useful.

1. you can use furrowed grass to break line of sight and draw in ranged enemies or set up surprise attacks.

2. one of your talents lets you see enemies within 3 squares, on the other side of walls and tall grass. Another lets you periodically get sight in an area. Both useful to surprise attack through tall grass.

3. warden subclass can see through tall grass like it's not there

For upgrades, a good usage of one scroll is to make two enchantment stones for free or spend energy to make an enchantment scroll and enchant the bow. Otherwise I save pretty much all scrolls for high tier equipment, barring a good ring drop