Final answer:
Pentheus does not perceive the stranger as having transformed; rather, he is driven mad by Dionysus in Euripides' Bacchae.
Step-by-step explanation:
In Euripides' Bacchae, Pentheus does not specifically think that the stranger (Dionysus in disguise) has turned into any creature or object. Instead, Pentheus is deceived by Dionysus and is driven to madness, which is part of Dionysus' plan to punish him for not respecting Dionysus' divinity and the rites of his worship.
Madness and transformation are recurring themes in Bacchae, not only for Pentheus but also for the women of Thebes, including his mother, who are driven to ecstatic frenzy and believed to have acquired supernatural abilities in their bacchic state.