Leareth would somewhat prefer not to do this via copious quantities of mind-control - it's not obvious to him whether the new arrivals are a hostile force rather than lost and in need of help - but they're understandably scared and being cautious. 

He does another compulsion. Answer my questions. At close range, it's even more obvious how weird the mind is, and - that it's not here, it's more not-here than the otherwise similar minds he feels from those of the creatures with horse-bodies. This...is a body it's wearing, or controlling at a distance, not its own form. But it's not like an elemental, native to another plane, summoned into a construct-body in the material plane. So where did its body go...? 

Focus. He needs to test if he can shield its communications first. :Tell me your name, please: 

<Arrelan-Sisokoth-Galar> what they can just control you without even taking your body that's horrifying they should just all kill themselves immediately - it attempts this -

Leareth, with even faster reflexes than Vanyel earlier, traps it in a stretchy force-shield.

He steps across to the other side of his barrier. He's keyed to it but the creature isn't, and so if he's right about the kind of shield required, he'll be able to Mindspeak it but not to hear its answer. At which point he can undo some of the compulsions. Maybe. 

:Tell me your name again: he sends. 

It says the same thing, again, while trying to batter itself with its wings.

Hmm, not quite yet, it's partially blocking it but he can still pick up the answer. Leareth pulls the floating force-barrier tighter so the creature can't injure itself, then spends a minute tweaking the shield and asks again. 

That time he can't pick up an answer. The bird is now contemplating whether there's any way to break off the connection to a morph - he's never heard of it but maybe just because it's suicidal not because it's impossible -

Leareth slips back inside the shield, and undoes all of the compulsions except the one to answer questions. 

:I apologize for kidnapping you: he sends. :I do not intend harm and I will let you return to your people soon. However, your arrival is relevant to my interests and so there is information I wish to have: 

He's picked up a number of fragmentary pieces, so far, but is still struggling to assemble them into a clear picture. 

:You are at war: he sends. :Is that right?: 

He's not going to help a Yeerk even if it's an offbrand Yeerk who has never heard of Yeerks.

<Yes> he answers anyway, involuntarily, and dislikes the honorary Yeerk all the more for it.

:I have a suspicion you are in the wrong place. You planned to travel to a - planet - called Earth, with humans on it, where you wished to gather information and possibly fight these Yeerks, but...you were expecting a more advanced civilization than Valdemar, correct?: 

<Yes. This isn't Earth.> The war is being fought on many, many fronts, though, and they still don't have much evidence that this planet isn't one of them even if it's not the one they knew about.

:I may be wrong: Leareth sends, slowly, :but I do not think the Yeerks are here. I would have noticed: He frowns. :Yeerks - control minds? With magic?: 

<Not with magic, unless the translation is unusually misleading. I do not know if you would have noticed. They have successfully infiltrated planets with mindreaders before. Yeerks are slugs. They crawl into the brain through the ear canal and control it directly from there.> And this bird HATES them and also him, the honorary one.

That's really fair of it, honestly. He doesn't bring up the fact that the new-arrivals have also been kidnapping and, he suspects, mindreading random humans. 

:It is possible they are somewhere in Velgarth: he sends, :but I am very confident they are not present either in Valdemar or among my people: Pause. :Did you intend to conquer, harm, or destroy the human civilization on this 'Earth': 

<We intended to stop them from falling into Yeerk hands.> Ideally by fighting the Yeerks but - his impression is that it didn't look that winnable.

Leareth closes his eyes for a moment, absorbing that. 

Somewhere, he doesn't yet know where, is an entire other world - somehow also full of humans, he's confused by that bit - and it's in danger. From an invading force of mind-controlling slugs, and from whoever these people are, sent to fight the Yeerks, and - the implication is clear, if they can't win Earth then they'll make sure no one can have it. 

(A flicker of memory - a Tower, a man pouring his life into fire and destruction to deny it to his enemy...) 

:Do you have the power to destroy this world, if that is the only way to stop the Yeerks from conquering it: 

<...not the planet itself, not very easily.> There would definitely remain a large ball of rock held together by gravity. 

:Do you have the means to kill all of the people on Earth: 

<Yes.>

Leareth takes a deep breath. 

:If there turn out not to be Yeerks on Velgarth, what are your intentions toward this world? What would your next move be?: 

<I'm not in charge.> He could speculate but the spell isn't quite forcing him to.

:Do you anticipate that your leaders might intend to harm or conquer the people of Velgarth, or - pre-emptively destroy this civilization in case the Yeerks come for it...?: 

<What? No. We would fix our ship and maybe try to learn the local - thing you're calling magic, we ought to be able to pick it up if we morph it - and then leave. Andalites do not conquer people. We might station ships in orbit to alert us if the Yeerks did find your world but you would be unaffected by them and unable to notice them. ...orbit is very far away> he adds as he realizes that these people may or may not be clear on their world being spherical.

:I know the world is spherical and suspected there could be others: Leareth clarifies. He's...reassured, somewhat, by that answer. 

He spends a moment thinking. 

:Listen to me, Arrelan-Sisokoth-Galar: he sends. :My name is Leareth. I apologize for my initial hostility and kidnapping, here, and understand that this will not leave you inclined to goodwill toward me. I needed to verify that you were not here to start a war of conquest against my world, and am now satisfied on that front. I am, however, deeply concerned by this war with the Yeerks that you describe elsewhere, and it would grieve me deeply if your people judged this Earth to be unsalvageable. So, I would offer you my aid and resources. I have a sizeable army and several hundred skilled combat mages, and am very motivated to help make this war winnable, if the alternative is the death of everyone on Earth. In return, I would request that you share how your advanced technology works: 

He pauses for a moment. 

:I am going to let you go in a moment, so you can return to your people and pass on this information. Your leaders can do as they wish with it. I am not staying here, but if you leave a message or a messenger in this place, someone will come to collect it. Do you have any questions?: 

He is thinking that it's an interesting philosophical question, whether the honorary Yeerks would be as bad as the original Yeerks if unleashed on the galaxy. Maybe they'd mostly fight each other. Probably not, nothing is ever that convenient. 

<No.>

:Then I wish you good luck: 

Leareth starts to remove the last compulsion, then pauses. :What are your people called? I would like a name for you, so I can stop awkwardly thinking of you as 'bird-possessing-creatures':