Regarding the initiative of creatures animated by the use of the animate dead spell.
Is it correct that if there is more than one creature, they share the same initiative? Or can they just be attached to their creator and take their turn on their creator's initiative instead?
The SRD says: "The GM makes one roll for an entire group of identical creatures, so each member of the group acts at the same time."
Note: the casting time for Animate Dead is 1 minute, so it's unlikely to occur during combat. But if it could, you might use the precedence from the many Conjure spells (like Conjure Animals), which say "Roll initiative for the summoned creatures as a group, which has its own turns".
Personal experience: despite the above, every group I've played with found it intuitive/easy to just handle these things on the caster's turn as a home rule.
By page 189 of the Player's Handbook, which is part of 5th edition's combat rules:
3. Roll initiative. Everyone involved in the combat encounter rolls initiative, determining the order of combatants’ turns.
Therefore every creature you summon with Animate Dead or other summoning spell has its own initiative and act on its own turn.
