Why does the Vagabond say other players told him about me? Can I send him to other players?

Solution 1:

Yes, the Vagabond is a part of the game and you indeed are able to send him to other players after dueling him. However the ability to send him after other players is not always an option

The Vagabond will occasionally show up in Duel World. If approached, he will remain mute, but will offer to Duel the player with a pre-determined "challenge" imposed on that player. These opportunities are beneficial for the player, as they will receive more character experience points than normal from Dueling The Vagabond, with the amount being dependent on the type of challenge they endured and whether they won or lost.

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Occasionally after a Duel with The Vagabond (regardless of victory or defeat), The Vagabond will remark, "That was an interesting Duel. Are your friends as skilled as you? If they are, I would like you to introduce me to one of your friends," whereupon the player is subsequently prompted to pick one of their friends and assign one of the above challenges.