Transitive Set Contained in Von Neumann Hierarchy Level

Theorem
Let $G$ be a transitive set.

Then for some ordinal $i$, $G \subseteq V_i$.

Proof
Suppose for the sake of contradiction that for each ordinal $i$ the set $G\setminus V_i$ is non-empty.

Let $i$ be any ordinal.

Then by the axiom of foundation:

$\exists x: x \in G\setminus V_i \text{ and } x \cap (G \setminus V_i) = \varnothing$

Then since $G$ is transitive, $x \subset G$, so $x \subset V_i$, so $x \in V_{i+1}$, so


 * $x \notin G \setminus V_{i+1}$.

Thus $G \setminus V_{i+1} \subsetneq G \setminus V_i$ for each ordinal $i$.

Let $H\colon\operatorname{On}\to P(G)$ be defined by
 * $H(i) = G \setminus V_i$ for each ordinal $i$.

Applying Strictly Increasing Mapping on Well-Ordered Class proves that for any ordinals $p$ and $q$, $p < q$ implies $H(q) \subsetneq H(p)$.

Since the class of ordinals is totally ordered, for any two distinct ordinals $i$ and $j$, $H(i) \ne H(j)$,

so $H$ is injective.

But that contradicts the fact that $P(G)$ is a set.