What? The only condition we know is that he has to defeat someone in order to completely seal them, not that he can seal them whenever he wants; that's not how it works.
I think there was a misunderstanding, because that's exactly what I meant
All we can infer is that physically overpowering and defeating someone seems to be a requirement but that's it.
It's unclear what the issue is, but his profile clearly states "tentacles" and not "shadow".
Because they are tentacles, they're just also made out of shadow. The distinction is irrelevant because they're all forms of his magic either way.
It's clear that Rossie had to go through a contract break and start to weaken after the club broke before he started using it regularly.
He was purposely trying to lose against the Vees and even then he still used it to hide from Box, and that was before breaking out of his deal.
Again Al was messing around against Adam and he got punished for it. You can see he's much more focused against 100% Vox just by the fact that he's not talking or trying to Aura Farm.
Either way it doesn't matter, Alastor is now free from his deal and has shown that he no longer fights arrogantly, so he'll simply do what's optimal.
Is it necessary? Yes, but transforming into a shadow is something he would do unless he was "immediately" swallowed or hit hard enough to injure him. Considering that shadow transformation is only used for "dodging" when necessary, it's not worth mentioning, especially not worthy of being a wincons
What do you mean "not worthy of mentioning"? You can't just sweep the fact that Alastor can just make himself untouchable to Pochita at any moment under the rug, it's a valid wincon that counters a lot of Pochita's own, such as LS diff.
And another thing, there are also breaks when using shadow transformation; notably, he doesn't use it frequently against The Vees and only uses it as a means of avoidance as mentioned above. He still gets punched by Valentino, still gets hit by Vox when both are in their base forms.
I said this before but I'll elaborate: Alastor was holding back here (mostly in terms of not using all of his abilities), he was purposely trying to be put in a situation where Vox believed he had the upper hand so he could trick him with a deal. Not by a huge amount, but still.
There's also the fact that this is his first fight after being weakened by Adam, so he's also testing what he can and can't do anymore. We see him struggling a few times to use his powers or being surprised by how much he's been weakened like when Velvette pierced his shield.
So him not using his shadow transformation frequently against the Vees can be explained by the context of the story. When he later fights 100% Vox, the only times he gets hit are when he's punched in the back or when Vox uses his own pseudo-teleportation. Every other time Alastor dodges and makes frequent use of his shadow form.