The Dragonborn can play tag with Grimvar. If talked to, he may ask to play a game (either tag or hide and seek). It doesn't earn any rewards, though.
When visiting Windhelm for the first time, Grimvar and his nanny, Idesa Sadri, are talking about Aventus Aretino and his performing the Black Sacrament in his home. Idesa quotes that Aventus Aretino is a strange child and she is the only friend Grimvar needs.
Grimvar says his father wants him to be a farmer or a sailor, but he does not want to be either of those and instead wants to be a warrior.
Grimvar: "Then it's true, what everyone is saying? That Aventus Aretino is doing the Black Sacrament? Trying to summon the Dark Brotherhood?"
Idesa: "Oh, Grimvar... always with the nonsense. No, no, of course not. Those are just tales..."
Grimvar: "Fine. Then I'll invite him out to play. He lives right there. I'm going to knock on his door..."
Idesa: "No, child! Wait! That boy, that house - they're cursed."
Grimvar: "Ha! Then I'm right. I knew it. He's trying to have somebody killed!"
Idesa: "All right. I won't deny it, child. What you heard is true. But Aventus Aretino walks a dark path. His actions can lead only to ruin. Now, enough. We will speak no more of this. I am the only friend you need.
- "All the Argonians at the docks are nice to me. Good thing too, or father would run them off."
- "Do you know my father? He's really important. He even talks to the Jarl sometimes."
- "They say dragons are coming back. I want to kill one!"
- Talk to Aventus Aretino
- If the Dragonborn casts a spell in the presence of Grimvar, Grimvar may ask the Dragonborn to make him invisible. The Dragonborn can deny the request or claim to have performed the Invisibility spell and even lie about it when asked for confirmation. There are no consequences for the actions.
- If The Dragonborn robs the Cruel-Sea home, Grimvar will hire thugs to "teach you a lesson."