Guide on adding a new model, animation, and creature to HoMMV

1) In my case, I give the Angels "strike from the heavens". But since they don't have a suitable "logical" Air Attack animation (and this ability performs it directly "standing on the target").

well, there are no animations, so where would new ones come from? the angel has neither a takeoff nor a landing, so either live with it, or learn to make animations, or find some workaround, sorry if my speech seems rude, I'm on edge today, and I can't be bothered to pick softer words

I want to use the Vengeance animation (falling sword). But then the question is — how do I get rid of the Angel himself in such an animation?

the terms here are wrong — Vengeance is not an animation but an effect in this case, it can be attached to the angel's animation, but the angel won't disappear — for it to look like what you described, you'd need an animation where the angel is hidden underground, and there's no such thing, so you can forget about it

I worked around this in my own way, it was a knight with a sword (not a vampire), the unit teleports with a black flash, for that I made an effect and sped up the animation... seemed nice... he quickly raises his sword and gets covered by a black blotch and teleports, strike from the heavens is the same thing, but with a really wild speed-up, he lingers on the enemy's model for a split second and then again with a black flash, so that the knight doesn't run out of the enemy on his own two feet, he basically moves by teleport

2) At the same time, not long ago I put Liches on T7, replacing the Bone Dragons. But even if I changed their animations, after death bones of the Bone Dragons fall out of the liches, i.e. it turns out the reference to this animation and effect work differently.

that's a simple question, you replaced the dragon's model and its animations, but didn't look into CreatureVisual

\GameMechanics\CreatureVisual\Creatures\Necropolis\Bone_Dragon.xdb
here's its contents, I've highlighted the line responsible for the death model

Header

<?xml version="1.0" encoding="UTF-8"?>
<CreatureVisual ObjectRecordID="1001205">
    <CreatureNameFileRef href="/Text/Game/Creatures/Necropolis/Bone_Dragon.txt"/>
    <CreatureAbilitiesFileRef href="/Text/Game/Creatures/Necropolis/Bone_Dragon_Abilities.txt"/>
    <DescriptionFileRef href="/Text/Game/Creatures/Necropolis/Bone_Dragon_desc.txt"/>
    <Icon href="/Textures/Interface/CombatArena/Faces/Necropolis/ico_BoneDragon.xdb#xpointer(/Texture)"/>
    <Icon32 href="/Textures/Interface/CombatArena/Faces/Necropolis/ico_BoneDragon_32.xdb#xpointer(/Texture)"/>
    <Icon64 href="/Textures/Interface/CombatArena/Faces/Necropolis/ico_BoneDragon_64.xdb#xpointer(/Texture)"/>
    <Icon128 href="/Textures/Interface/CombatArena/Faces/Necropolis/ico_BoneDragon_128.xdb#xpointer(/Texture)"/>
    <AnimCharacter href="/Characters/Creatures/Necropolis/BoneDragon.(Character).xdb#xpointer(/Character)"/>
    <DeadCharacter href="/Characters/Creatures/Necropolis/BoneDragon_Death.(Character).xdb#xpointer(/Character)"/>
    <AnimShot/>
    <SummoningEffect/>
    <DamageEffect href="/GameMechanics/CreatureDamage/Necro_Hits2.xdb#xpointer(/CreatureDamage)"/>
    <TeleportingMove>
        <Use>false</Use>
        <StartEffect/>
        <FinishEffect/>
    </TeleportingMove>
    <Win3DView/>
    <MountPoint>
        <x>-0.324112</x>
        <y>-0.0439671</y>
        <z>1.19451</z>
    </MountPoint>
    <MountBone>Neck_1</MountBone>
</CreatureVisual>

for some zombie this line is written differently, without a reference to the model, this is needed for complex models that break apart into pieces after death

and rooting is hardcoded in the engine, only one creature can root