There is no more 9-tailed Sparkleaf; there is only the 7-tailed Sparkleaf, and also the one-tailed Sparkleaf. As of July 15, 2016, the following information is current:
7-Tailed Sparkleaf
This is Sparkleaf's "true" form, so to speak. A feral kitsune, he displays his seven tails, tipped green to indicate his bond with nature; the five markings on his face indicate his servitude to Inari. Naturally, this is also the form in which Sparkleaf's fox powers are strongest.
In the past, Sparkleaf displayed his seven tails proudly and freely. Now, he safeguards this form more carefully, reserving it for special occasions such as staff banquets, and typically does not reveal it in public.
One-Tailed Sparkleaf
Sparkleaf's everyday form. Illusion conceals both his facial markings and his multiple tails, so that he merely appears to be a strangely-colored fox. To Sparkleaf, this one-tailed illusion is akin to part of his clothing.
Note that he does NOT merely hide six of his tails; all seven tails are seemingly converged into one. Should his tail be injured, his real tails will share the damage. However, it allows for much greater mobility and convenience. His tail is seven times as strong as a normal fox's, but he would not quite match the power output of another seven-tailed fox.
Bipedal Sparkleaf
Only with a biped body does Sparkleaf retain the long scalp hair of a Ninetales. Just like with a quadruped body, he generally stays in one-tailed form, especially when wearing dragoon armor. However, he could theoretically appear seven-tailed and bipedal...
Bipedal Sparkleaf is comprised of multiple layers of illusion, sacrificing magical potential for agility and physical skill. Naturally, this is his preferred form for battle. However, it is also the most vulnerable to illusion-breakers.
Other forms
As shown, Sparkleaf has seasonal forms, though they may not necessarily feature his markings. The winter form is now the only time his tails are 100% green. Additionally, as a staff member, Sparkleaf must sometimes employ various disguises, including foxdoge and Magical Vixen Sparkles.
The ordinary red fox is sort of a public appearance, sort of a "shorthand" Sparkleaf. On Facebook, Tumblr, Twitter, and some other places, I represent Sparkleaf/myself as a normal fox for convenience's sake. At the same time, the 7-tailed form is still more detailed, and thus more symbolic for me-- the "unabridged" Sparkleaf.
I have this weird theory, see, that a kitsune secretly only has one tail and that this one tail is just capable of occupying multiple spaces at the same time as the fox grows older. And when writing, I actually visualize things as if Sparkleaf only had one tail, then later change the wording to acknowledge the multiple tails.
maybe it was too early to show the dead sparkleaf one