Despite its (maybe outdated) tooltip, Corrupted Grass can definitely not be found anywhere on the Corruption layer, nor can it be discovered anywhere else on Creativerse game worlds, since it is not generated "naturally" nor is it part of any template world.
Dead Grass, Tallgrass and Savannah Grass cannot be corrupted, neither by Corrupted Water, Corrupt Obelisks nor by Corrupt Bombs. While common Dirt will turn into Grass when touching other Grass blocks and "under the sun", Corrupted Dirt will not change into Corrupted Grass.
On blocks of Corrupted Grass, any type of Corrupted Creatures can randomly spawn in darkness, like Corrupted Pigsies, Corrupted Leafies, Corrupted Rocksters, Corrupted Chizzards, Corrupted Mirus and Things. Also, Diamond Treasure Chests can randomly spawn on these blocks in darkness.
How to obtain
After creating Corrupted Grass by corrupting green Grass blocks, these blocks can only picked up with either a Diamond Mining Cell or Lumite Mining Cell equipped. Both Power Cells will lose durability when pulling Corrupted Grass. If you want to use Excavators, you will need to place a Super Excavator in order to remove and (save half of this amount of removed) Corrupted Grass.
How to use Corrupted Water
Blocks of ordinary green Grass can be corrupted by placing Corrupted Water ledge to ledge with (green) Grass blocks. Corrupted Water will not corrupt blocks diagonally (corner to corner), but only up to 6 adjacent Grass blocks to each side, below and above a placed unit of Corrupted Water. It can take quite a while until Grass will turn into Corrupted Grass while being transformed by Corrupted Water.
Corrupted Water requires at least a Diamond Mining Cell (or a Lumite Mining Cell) for scooping. This will reduce the durability of the Power Cells. Corrupted Water can be found on the Corruption layer deep underground (the deepest layer of any Creativerse game world), or can be made from ordinary Water by throwing Corrupt Bombs at it.
How to use Corrupt Obelisks
Corrupt Obelisks can be crafted after their crafting recipe has been unlocked for free. They are signs in principle, but can also corrupt ordinary green Grass blocks much like Corrupted Water can. They cannot corrupt any other types of blocks (anymore) though.
Simply place Corrupt Obelisks on and/or next to Grass blocks, then they can corrupt up to 5 blocks of Grass - to their sides (not diagonally) and below. This will take a little while and is going to happen no matter if the Corrupt Obelisk is wired and/or activated or not.
How to use Corrupt Bombs
It seems that the maximum of blocks that Corrupt Bombs can affect at once is an area of 5x5x5 blocks (only Grass, Dirt, Stone, Water, nearly all types of Wood and nearly all types of tree Leaves), while the minimum area that Corrupt Bombs will corrupt usually is 5x5x2 blocks in size.
To use these Explosives, put a stack of Corrupt Bombs into any slot of your quickbar, select this quickslot and use right-click to throw one of these bombs at the spot you're aiming at with your crosshair cursor.
How to use Corrupted Grass
Corrupted Grass can be used for building (for example corruption arenas) or for decoration purposes.
By getting closer or standing next to/on blocks of Corrupted Grass, a Corruption gauge will be brought up and start to fill itself with violet color. Should the Corruption gauge completely turn violet, Corruption damage over time will be dealt to player characters and also to Creatures if they are exposed to Corrupted Blocks long enough. Corrupted Creatures and a few other Creatures are immune to Corruption though.
Corrupted Grass will not spread Corruption to any other blocks nor liquids (anymore).
If blocks of Corrupted Grass are put on display on Placemats, Stone Wall Shelves, Frozen Containers, Snow Buried Containers, Hidden Temple Altars, Galactic Grav-Chambers or the like, they will not bring up the Corruption gauge nor will they cause any Creatures or Treasure Chests to spawn.
Preventing Grass from turning into Corrupted Grass
The transformation of common Grass to Corrupted Grass can be stopped by claiming the area and disabling the advanced claim option "Corruption Sim Enabled". In this case, Corruption will not spread from Corrupted Water to Grass, nor from Corrupt Obelisks, nor will thrown Corrupt Bombs be able to transform any blocks (or Water) on the claim where the corruption sim is disabled. Corruption can also be disabled for the whole game world by the world's owner ("Disable Corruption Spread"), which will also affect Corruption spreading from Corrupted Water and Corrupt Obelisks as well as the effect of Corrupt Bombs.
Please note that disabling Corruption spreading will neither stop the Corruption gauge from showing up, nor Corrupted Creatures from spawning, nor Corruption damage taken. This claim and/or game world option will also not "purify" any already Corrupted Blocks nor Corrupted Water.
Super TNT can destroy all Corrupted Blocks, including Corrupted Grass.