I've had a few...
I've always imagined myself reverting back to the age of 13 or 14, but with my genitals reshaping themselves to those of large stallions (meaning I can knock myself out with an upward swing of my own horse dick)...but I also have this insatiable thirst for fresh milk from a large mammalian creature, and I mean straight out of the source.
I would lurk in the shadows, searching for such a female, and I've had 2 or 3 forms that I favored above others: the form of a curvaceous woman (bordering on BBW with big breasts, big butt, wide hips and big thighs), a large mare with rather wide hips and really heavy thighs/flanks, and a large cow with an extremely short-trimmed coat, but with a gigantic, milk-swollen udder, in need of milking.
How I capture my quarry? While they go about their business, unaware of my presence, I sneak up from behind and underneath. Sneaking through the tall grass, taking as much care to make sure my own genitalia do not get knicked by the sharp edges of the grass, I inch closer and closer to the targeted female. As she slowly stumbles closer into my grasping range, I lunge; my mouth seizing onto one of her nipples/teats as my arms wrap tightly around her body. She'll gasp and call out in surprise, but frozen and paralyzed by the sensation of her milk glands getting sucked on.
Breathing in my pheromones, she'll instinctively wrap her arms around me as she becomes imprinted upon me. Totally enthralled by her new surrogate "offspring" nursing from her mammaries, I walk her back to my own lair. By this point, she's totally consumed by euphoric arousal and is totally ready for the big fuck. With the greatest of ease, I set her down onto the sleeping mat, and I bury myself deep inside of her love tunnel. Since my restructuring was done through magic, it only makes sense that magic is involved with this coitus, and assists in allowing the woman in taking every last inch of my stallion dick inside of her. Consumed by the orgasm and euphoria of having her breasts being sucked on by a smaller form, the final phase is the insemination. Cumming deep inside of her, I flood her entire uterus with the enchanted seed of my chimeric penis. Her belly distends a bit as her uterus swells with this inflow of semen. The spell is complete; she is now...mine.
Seems like I focused on the woman on this one. Well, a similar scenario would unfold with the mare and the cow. The spell is initiated the instant I seize upon one of her teats and suck on them like a starving foal. At the end of the day, whoever and whatever I choose for a sex thrall, she'll treat me as if I was simultaneously her own child and mate. I love women that dote upon me as if they were my own mother, and it would be an interesting feeling to experience a mare or a cow doting upon me and hovering over me as if they just gave birth to me.