Mashed Tails

In contrast to his personality in the original Sonic franchise, the Tails of the Secret History universe is an unhinged psychopathic sadist, who’s completely fixated on the idea that he’s Sonic’s only best friend and will murder anyone in the most brutal way possible if they try to be friends with Sonic. He claims to be doing this because Sonic's other friends are "impostors" - Tails claims to be Sonic's best friend. He is most likely a yandere due to his Sonic obsession, to the point where he identifies himself as Sonic's “best friend” to the point he may be in love with him and want him all to himself.

He is also shown to be manipulative, using Amy and Sonic to make the former insane and kill the latter during a breakdown, knowing Amy's obsession with Sonic is similar to his.

Despite all of this, all Tails wanted deep inside the whole entire time was to win Sonic's affection and appreciation, which this incarnation of Sonic is able to offer him, as he doesn't find him nuisance.