Scary Monster

Scary Monster (スケアリー・モンスター) is an ability featured in Part VII: Steel Ball Run, seen as part of the stand Scary Monsters (plural). It is named after the David Bowie album Scary Monsters (and Super Creeps). 

Appearance/Personality
It can be debated that Scary Monster is not a true stand but the after effect of the stand Scary Monsters, that it lingered and somehow fused with Diego Brando because of the use of his Turbo Eye. The appearance is based on how much Dio is changing but it always retains a black tail with the words 'Dio' repeatably written on it.

Powers
Morph: Dio is capable of changing his body from that of a human to that of a half-dinosaur, fully fledged or partial part of it. While in his morph status he has an increase stamina, strength, speed and vision along with capable of eating anything. Much like Dio's original vampire form, it far surpasses human limit, but without the sunlight weakening Dio also seems to have the ability to morph other creatures into dinosaurs as well, similar to the original, Scary Monsters, Stand. This was shown when Dio combined powers with Sandman in order to attempt to defeat Gyro and Johnny.

Transmute: Dio discovered this feature of his power only in the last stages of the race, he practically can use this ability to turn anyone he touches into inanimate wooden objects like candle-holders. Note that all this objects are dinosaur themed. Furthermore, by exploiting this power, Dio can assume a person's appearance, just like Cream Starter or Benjamin's Stand would. He seems however to have to kill his target to assume its identity.

Hand to Hand: Perhaps the most curious and unique ability of Dio's power. Being bound to his body, Scary Monster allows him to fight in first person against other Stands and physically damage them, whereas normally Stands can be damaged only by other Stands.