What is missing?

A dick

A smile played across your lips. "But can you grow a dick to dwarf mine?"

"Is that a challenge?"

"Absolutely."

With a grunt, she thrust forward her hips. Her clit began to grow outward, longer and thicker, becoming a sizable shaft and then some. It capped its growth at a foot long, flaccid. Two cantaloupe-sized balls hung down at her crotch, churning with seed as her shaft started to harden at the sight of you.

You decided you wanted to go further. "How about two?"

Another groan rumbled out from her enormous chest as another cock pushed out from her groin, to the left of her original manhood. Another set of equally large balls swung down, knocking against the original pair, making her crumble to the ground.

"Come on," you taunted. "You can't be that weak, can you?"

"I'm not!" she growled, pushing herself off the ground. Her balls swung against each other as she moved, but this time she didn't falter. Her skin began to darken, as if made of tough leather. "Now nothing can make me weak again. I'm indestructible."

"But I bet there's one thing you can't do."

She nearly ground her teeth to dust at that statement. "What would that be?"

"I bet you can't ruin me. Sexually, at least."

"Is that a challenge?"