I would rather prefer Tikal having her funny blob feet, but there will obviously be times where I'll give her humanoid feet to fit foot fetish situations like this one.

Knuckles has repeatedly lost the Master Emerald under different circumstances as it's current and only protector on Angel Island. Still very diligent and determined, he makes sure to always re-gather the Master Emerald shards since they scatter all over the world upon it's destruction which is done as a failsafe to prevent evildoers from obtaining them like Eggman for example or rivals like Rouge getting in his way. Knuckles can sense the location of both the Master Emerald shards and the Chaos Emeralds. Unfortunately for him, so can Rouge.

Tikal seeing his performance started getting concerned about his skills to guard the emerald so she approached him through a portal and planned to relieve him of his duties of over the emerald since it came close to falling into dark hands a few times. Knuckles felt angry about this and wanted her to test him to continue seeing if he's worthy to protect it. Tikal agreed and decided to place him under an ancient echidna trial that her tribesmen had to go through to earn the right to protect critical items or people.

Knuckles gave her another idea for a trial, he wanted to scale her body...primarily her feet. Weirded out by this she urged him to do ancient trial instead. He then mentioned to her that she secretly had a tribal warrior she liked do this sometime during her life in place of the actual trial. Embarrassed by this and confused by how Knuckles knew about this specific part of her life, she gave in to avoid further embarrassment and allowed this weird trial to happen. She sat down, used her magic to shrink him down to a barely visible spec and placed him at the heel of her huge Mobian feet.

Fortunately for Knuckles Tikal keeps her feet clean so he began ascending them. It took a while due to how small she shrunk him, but in the end he prevailed. Passing the test, Tikal returned him back to normal size and continued giving him the privilege to watch over the Master Emerald. Tikal will still come to the present often to check on him and to see everyone else.

She told Knuckles to keep this a secret. If he tells anyone she threatened to trap him inside of the Master Emerald. He, smirked, gave her a head pat and glided off into the distance as she watched.