When I was 10 years old my mother purchased my brother and I the Magic The Gathering Official Encyclopedia
At full power, it becomes a huge creature that drains each opponent for 2 life whenever you sacrifice a land
They enter the battlefield tapped, and their three-mana cycling cost is on the slightly more expensive side, but the chance to access three different mana pools and card draw with one card is worth it for many different decks
A fun strategy in casual Commander involves putting your life total as close to 0 as you can, then swapping it with an opponent's high life total with cards like Mister Negative, Reverse the Sands, and Axis of Mortality
At the beginning of each combat, if Reservoir Kraken is untapped, any opponent may tap an untapped creature they control
Midrange decks are much more interested in playing powerful singular threats and gaining card advantage than pressuring an opponents life total