Corrupted Ashenwood Leaves cannot be found as "naturally" generated Corrupted Blocks in any game world, these special Leaves can only be made by players.
All kinds of Corrupted Creatures as well as Diamond Treasure Chests can randomly spawn on Corrupted Ashenwood Leaves (and on any other kind of Corrupted Blocks for that matter), as long as the area is not illuminated by artificial lighting or sunlight. Corrupted Leafies are quite rare, but they still spawn well enough on artificial arenas/platforms made from Corrupted Leaves of any kind.
How to obtain
Uncorrupted Ashenwood Leaves can be taken from birch-like Ashenwood trees that can be found in Woodlands, in Grasslands, near Mountains, in a small bush-like size in Canyons and Savannahs, or can be grown from Ashenwood Saplings. Harvesting ordinary Ashenwood Leaves does not require any Power Cell to be equipped.
Of course you won't be able to pick up such blocks on game worlds, on player claims or in Adventures where your Permission rank is not sufficient (mainly when you are merely a visitor), which can only be changed by the owner of the game world, the respective claim owner or Adventure creator.
Corrupted Ashenwood Leaves can be bought as parts of (customizable) building kits for any customizable Blueprint with Coins, which in return are purchasable for real money via Steam Wallet in the ingame Store. You can use Blueprints that you have captured yourself with Capture Blocks, as well as Blueprints that were made by other players and that you have subscribed to in the Steam Creativerse workshop, or Blueprints that you have customized with Corrupted Ashenwood Leaves.
To buy a building kit, either select the according Blueprint or activate a cornerstone that has been placed into the game world (and has optionally been customized). Check the content of the block kit first by clicking on the description "Built with xxx Blocks" before you'll click on the green price tag button below "Get kit and build now".
Corrupted Ashenwood Leaves cannot be obtained from any Creature nor from any randomly spawning Treasure Chest. Corrupted Ashenwood Leaves are also not part of any seasonal game content, Store bundle, seasonal minigame event reward or NPC trade offer.
It is not possible to grow corrupted Ashenwood trees from Saplings.
Corrupting Ashenwood Leaves and purifying Corrupted Ashenwood Leaves
All uncorrupted tree Leaves (as well as uncorrupted Wood blocks, but not Logs) can be corrupted by throwing Corrupt Bombs at them. One Corrupt Bomb can corrupt 5x5x5 blocks at maximum, often only 5x5x3 though.
Corrupted Ashenwood Leaves can be purified by placing at least one Healing Beacon on them or nearby or by throwing Purification Bombs at them. One Healing Beacon can purify Corrupted Blocks (and/or Corrupted Water) in the range of two blocks to each side, but also downwards and upwards plus the one block that the Healing Beacon is placed on, and one block diagonally to all sides. Purification Bombs can purify up to 7x7x7 Corrupted Blocks at maximum, usually only 7x7x4 though.
Please note that Corruption can be disabled on game worlds and separately on player claims by world options and claim settings (claim settings override world options). If Corruption spreading/sim is disabled, then Corrupt Bombs, Corrupted Water and Corrupt Obelisks will not corrupt any corruptable blocks on the affected land at all.
It's also possible for the Corruption spreading/sim option to influence purification - if Healing Beacons should not start purifying Corrupted Blocks or Corrupted Water after 30 seconds, then try switching the Corruption spreading/sim option on and off again.
How to use
Corrupted Ashenwood Leaves can be placed directly into the world as solid blocks for building or decoration; however they can make Corrupted Creatures spawn on them during day in unlit areas and during the night in darkness.
You can fully rotate Corrupted Ashenwood Leaves into all directions by pointing your cursor at them, then pressing and holding R (as the default key) and then moving the mouse while holding down the left mouse button. The chosen rotation angle can be "locked" too by simply typing "r" while looking at an already rotated block or item, so that all blocks of the same stack in the chosen quickslot will then face the same direction when being placed.
Corrupted Ashenwood Leaves make excellent Fuel for the Forge with a good heating factor of level 3, providing rather quick forging progress, even though 4 Corrupted Ashenwood Leaves blocks have to be used up at a time for each process of smelting, baking, melting or hardening.
The only better fuel is level 10 Food: Tar Bread, Tar Sandwich and Tar Soup. Corrupted Wood blocks are also level 3 fuel types just like Corrupted Leaves, while Coal, Hardened Lava and Sulfur are level 2 fuel, and all types of plants, uncorrupted tree leaves, uncorrupted wood blocks, logs, wood rods and several crafted wooden objects are slow-burning level 1 fuel.
Corrupted Ashenwood Leaves can also be put on display by placing them into the slots of display containers like Placemats, Stone Wall Shelves, Hidden Temple Altars, Galactic Grav-Chambers, Frozen Containers, Holiday Decorative Trees, Snow Buried Containers, Holiday Mantles, Wood Planters, Flower Pots or the like, where they will be reduced in size and cannot be rotated, purified nor burnt.
On artificial "biomes" (such as platforms of only 1 block "height") made from a large enough amount of Corrupted Ashenwood Leaves, not only all types of Corrupted Creatures, but also valuable Diamond Treasure Chests have a chance of spawning when in complete darkness.
Corrupted Ashenwood Leaves cannot be processed in Processors.
How to get rid of tree Leaves
Super Excavators can remove up to 7x7x7 Corrupted Ashenwood Leaves blocks at once and save half of these blocks in their (usually 3) loot bags.
Destroying Corrupted Ashenwood Leaves completely is possible by using the AOE Gauntlet Smash attack of your ArcTek Gauntlet when you have at least 75% of your maximum Stamina (either 75 for F2P players or 150 for "Pro" players, or more if you consume Stamina-enhancing Food) - by hitting the Leaves from above (it's a ground smash that will only affect 1 block upwards at most). This will remove Corrupted Ashenwood Leaves up to 2 blocks to the sides and downwards from the point of impact without leaving anything behind.
Corrupted Ashenwood Leaves can be destroyed this way even without any Power Cell equipped. Power Cells don't lose durability when the Gauntlet Smash is executed.
You can alternatively destroy Corrupted Ashenwood Leaves by using Super TNT, and you can burn Corrupted Ashenwood Leaves to nothingness by throwing Fire Bombs or Flaming Skulls at them. This can burn 7x7x7 blocks of Leaves at max. instantly (usually only 7x7x4 though).
As long as the fire spreading option of game worlds is not disabled (enabled by default), placing several torches or any other items with open flames or fiery blocks like Hardened Lava directly under blocks of Corrupted Ashenwood Leaves is somehow dangerous as these Leaves blocks can catch fire (albeit reluctantly) and burn to nothingness in hot environments that make a heat meter/scale show up, like Oceans, Jungles or the Lava layer, but also in much cooler Swamplands.
Usually, only one torch or the like is not hot enough to start a raging fire, but placing many heat-emitting objects together will boost the dangerous chances. Liquid Lava, Fire Bombs or Flaming Skulls will immediately set Corrupted Ashenwood Leaves blocks on fire.
If Corrupted Ashenwood Leaves blocks start burning, the flames are then able to spread to other nearby flammable blocks, even across gaps of 1-2 blocks on game worlds and player claims where the "fire spreading" option is enabled. This way a whole wooden building or forest (especially Weepwood trees, Wildwood trees, Parchwood and Shorewood though) can burn down in the worst case.
Fire cannot be extinguished by using liquids, but it can be stopped from spreading by claiming the area and making sure that the claim (advanced) option "fire sim/spreading enabled" is disabled (by default). Fire Bombs (and Flaming Skulls) will have no effect on these claims either.
It is also possible for owners of the game world (F2P players included) to toggle the spreading of fire on a whole game world in the basic world options ("edit world" and "disable fire spread"), which will also render Fire Bombs and Flaming Skulls useless there. Another option to stop fire from spreading would be to create forest aisles/swaths wide enough so that the flames cannot leap over.
In earlier versions of Creativerse, it was possible to corrupt most uncorrupted tree Leaves by pouring Corrupted Water on them or placing them into this liquid, but this is no longer the case.