The Ring is found in the Sandpits. The player must fall into the whirlpools until one of them takes them to a cave inaccessible on foot. The very first one when entering the Sandpits does this. In the cave an NPC will sell items, and gives the player the Jaguar Ring if they buy at least one item from them.
The Jaguar Ring allows the player or dog to sprint by holding A and moving. Sprinting is much faster than running, but rapidly drains the player's weapon power. When weapon power reaches 0%, they will stop running so power can recharge.
As soon as the player or dog starts sprinting, their energy % is halved and then runs out by 20% per second. At 0% the player can still sprint but only for a few frames. This is a commonly used feature in speedruns and advanced players.
This also means that the player can run indefinitely by using a weapon at weapon level 3. Charge up to at least 201% (the level 2 bar and 1%), then begin sprinting while holding both B and A. The initial sprint will drain half the energy %, but it will remain above 100%. As long as B is still held down, the weapon will charge faster than sprinting drains it, allowing the player to run indefinitely.