A lizard

You had decided to combine him with a lizard. You had the man strapped naked onto a table. He was a little difficult at first, but after you cast a dizzy spell on him he was much easier to handle. The ritual could begin.

You collected a lizards tail and placed it on the man's stomach. You placed your hand over it and summoned your magic. This put an ethereal glow over your subject. The man started to become worried and asked "What are you doing?"

You chose to ignore him and continue the spell.

"Stop it." He said softly.

You continued to ignore him and persisted the spell.

The man began breathing heavily. He felt something was happening to him.

"Stop it! Stop it, please! Somebody, help me!" He tried to say. He was too dizzy to resist at all and was completely at your mercy.

Finally the preparations were complete. The merging could begin.

The man's stomach became like liquid, allowing the lizards tail to disappear into it. While it was absorbed by the man's body, he started to change.

Green scales started to grow all over his back. From there it spread to his shoulders and the back of his arms. It also spread to his butt and downwards along the back of his legs.

After that, his hands and feet adapted. They grew bigger, stronger, and his nails changed into claws.

Then he grew a long scaly tail.

The last thing to change were his eyes, where his pupils elongated.

Once that was done, the merging was complete. You ended the spell and retracted your hand.

You had turned the man into a lizard-boy.