While this ability is very powerful, Gwenom, Remorseless isnt perfect
Seafloor Oracle If card draw is what you're after, Seafloor Oracle is your best friend
Also, when Grimgrin attacks, you get to destroy a Creature the defending player controls, and then put a +1/+1 counter on it
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
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