Within a Treasure Chest in the Sword & Shield Maze.
Link won't be knocked back as far when attacked.
"Get knocked back less"
The Steadfast Ring is a Magical Ring that Link acquires in Oracle of Seasons. There is no possible way to acquire the ring in Oracle of Ages directly, but it can be acquired by using the Ring Secret.
In Oracle of Seasons Link can find the Steadfast Ring in a Treasure Chest within the Sword & Shield Maze. From the entrance of the dungeon, walk up one screen, and then head up another screen along the right side of the room. There are three torch statues on the lower area to the left. Stand on the higher platform and use the Hyper Slingshot to shoot three Ember Seeds at once to hit the three statues, causing a Treasure Chest to appear. Jump over and open it up to get the Seed Ring that becomes the Steadfast Ring when appraised.
When equipped, the Steadfast Ring lowers the distance that Link is pushed back after enemy attacks. This ring has particular use in certain Boss or Mini-Boss battles where holes in the ground are one of the obstacles to avoid. However, for some players, this could have a negative effect. After being hit, Link is pushed away from the enemy to prevent consecutive hits. When wearing the Steadfast Ring, Link won't get pushed very far away.