During gameplay, a player may choose to attack any other player, regardless of their position on the table, and can also choose to attack multiple different players during their attack phase
Since most Hydras don't have generic costs to reduce, this mana is instead automatically pumped into the X section of a Hydra's mana cost, essentially giving it a free power and toughness boost
Cards like Cloud, Ex-Soldier, Gilgamesh, Master-at-arms, and Firion, Wild Rose Warrior, are great at pulling out the best of Equipment, boosting creatures to a ridiculous degree
You can make, in Mono-Green alone, 1/1 Squirrels, Insects, Saprolings, 2/2 Wolves, Bears, 3/3 Centaurs, Elephants, Beasts, from Squirrel Nest to Grizzly Fate to draw tons of cards