My guess is that his physical form had long since vanished; what we saw was his human form as magical essence, like a magical imprint of his soul, but because he didn't have a body in which to contain himself, it dissolved.
But he did have a body.
Here is it thudding against the very real ground.
And here is Zoldeo claiming loud and clear how it's his original body.
You're making shit up.
I don't see how his power is senseless. He controls humans. Period. As for why he's in Capricorn now, it's simple. Capricorn wanted to go be with Lucy, since that's what Layla had setup.Zoldeo changed his mind and didn't want this, so he tried using his subjugation magic on Capricorn to make him stay. The spell backfired, as Capricorn was a spirit, and it fused Zoldeo's spirit/essence into Capricorn's body. Was that really that hard to understand from reading the chapter?
That part is all fine and well. You still danced around the question: Why kill Lucy now?
Because here is a big thing: Capricorn NEVER made a contract with Lucy. Rather he only made a PROMISE to her mother. If Lucy made an actual contract she would have his Key. As demonstrated here.
If Capricorn's "pact" with Lucy's mom was worth anything, Lucy's mom would have her key. Not even Lucy has it. Let's not overlook that that pact would be broken if anything since Lucy's mom is DEAD.
So if anything, it would be Capricorn's attitude which could have possibly pissed Zoldeo to possess him. And even then, he could just dismiss him. It still makes no sense.
Ah, but Zoldeo is not a Stellar Spirit Mage, per se,
He is. Capricorn refers to him as a "user".
and was not the owner of Capricorn.
He is. They made a contract.
He uses Human Subjugation magic. As such, Layla, and now Lucy, were the only people that could summon or dismiss him. If he kills Lucy, by the laws of the Stellar Spirit Mage, he becomes the owner of Capricorn.
Three things:
1. He doesn't have to kill Lucy to become Capricorn's owner. Lucy proved this when she took Virgo. A stellar spirit can break contract without the death of the owner.
2. Capricorn was out of the Spirit world 17 years. This means he possesed Capricorn before Lucy could even use magic. This means Zoldeo summoned Capricorn UNDER HIS OWN CONTRACT. This also means as Capricorn, Zoldeo kept Capricorn in this world, instead of him fading away like Loki was going to. This is probably why Mashima used that cliche ass "fell into darkness" line instead of just saying "He didn't want me to go to Lucy because he thinks im rly kool, so he used his majiks on me"
3. It's against the rules for a Stellar Spirit to kill a human, or they get stuck in the human world, until they fade away. Isn't this what happened to Loki? If Capricorn kills Lucy, he'll be unable to dismiss himself. Hell, he's probably unable to dismiss himself now. It's not a stretch to believe he has killed since joining Grimore Heart of all guilds.
(Remember how Angel took Karin's keys after killing her?) So, his theory was that if Lucy was killed, Zoldeo would finally be able to dismiss Capricorn, and would return to his own body.
Alright alright time out.
For one, …. no.
If all he had to do was go to the spirit world to separate himself from Capricorn, he would have just done it. Spirits can come and go at WILL. Capricorn and Loki did it THAT CHAPTER.
Secondly, if he wanted to break Lucy's contract, he could. Hell, he could just use a human with his magic and make a new contract and recall himself.
Lastly, it seems like he didn't even care if he got his old body or not. He seemed perfectly content in Loki's body, and even entertained the thought of turning her into a (love)slave.
He treated the return to his body more as a consolation prize more than anything else. Before he disappeared that is.
However, after being forced out of Loke's body, he quickly found out that his real body was gone after he had fused with Capricorn so long ago.
And we have no idea why.
Lastly, the power transference isn't that much of a stretch. What do you think healing magic is?
Magic of healing?
Wendy's specialty?
The whole reason the OS kidnapped her?
It's transferring power from one character to another to heal their wounds. If healers can do it, most mages should be able to transfer power, at least partially, to another mage temporarily.
No it shouldn't. It defeats the purpose of Wendy altogether, especially since Mashima made her healing so limited.