Hvastania

Mobs

All hostile mobs (zombies, skeletons, creepers, spiders, witches, Endermen, the Wither, etc.) have double the health, damage, and speed.
This effect does not apply to the Ender Dragon, slimes, or ghasts.

Blocks

All blocks take 10 times longer to break.

Items and Armor

Tools and weapons lose durability 5 times faster: each time a block is broken or a hit is landed, an additional 4 points of durability are consumed.
Armor wears out 5 times faster when taking damage.
Bows, shears, and other items that do not involve breaking blocks or landing hits are not subject to this mechanic.

hvastans-Plants

They spawn in the Overworld, the Nether, and the End, on any type of block—including inside caves.
One plant appears every 5 seconds in approximately half of the loaded chunks (up to a maximum of 40 plants per chunk).
They do not spawn within 2 blocks of the player.
Physical contact inflicts Slowness, Poison, Nausea, and Weakness for 30 seconds.
Picking the plant results in death—even in Creative mode.
the block can be found in the 'Decorations' tab in the Creative inventory.

Known limitations

Spawn locations are chosen uniformly across the height range, so many plants appear underground.