Vecna’s Link. 

You gain a special intuition for secrets. You have advantage on Wisdom (Insight) checks. In addition, you can use an action to cast See Invisibility without expending a spell slot. Once you cast that spell in this way, you can’t do so again until you finish a long rest.

The Power of Secrets

Learning Secrets.

Every time the party learns a powerful secret, note it on the Secrets Tracker. Once the party learn a secret, they can’t learn it again. When one character learns a secret, it counts as a secret learned for the whole party.

Revealing Secrets.

A character can magically spend a secret like currency, revealing it to the multiverse to gain a momentary boon. To do this, the character must use an action to whisper the secret into the wind. The secret is then gone from the minds of every character in the party.

When a character spends a secret, every character in the party gains advantage on d20 rolls for 1 minute.

The characters might hear the information from the secret again, but they can’t spend a secret more than once. If the party shares a secret with anyone not in the party, that secret immediately loses its power and counts as revealed. It remains in the minds of every character in the party, but the characters gain no benefit from revealing the secret.

Keeping Secrets.

While the secrets can be used as described in Revealing Secrets section, the party has an intrinsic knowledge that secrets are a source of power far greater when in proximity to Vecna's ritual, and will grant additional benefit if kept. The number of secrets learned and unspent will be tallied when you confront Vecna. The more secrets you have, the greater the boon you will receive.