Riot... did you code the Nexus as a Minion... again?

You're both bring up some good points!

The way everywhere buffs work is like this:

1. Give the buff to everything exists right now (what you called out)
2. Put a script on the nexus which handles any future things that should get the buff, that don't currently exist. A new poro is generated by a card, it'll get the buff from this nexus script.

So everywhere buffs are technically not aura effects, but they do have that additional listener on the Nexus for things that haven't come into existence yet.

There are other effects that are persistent auras (some Path of Champion powers, persistent auras like Deluge, Zoe's effect, etc...) and those are scripts on the Nexus, and just like any other aura, if the holder card dies... the aura drops off.

Yep! That is exactly right. I'm trying to think of a scenario that would repro that... I think something like:

1. Your Nexus is 1 HP and you have a Braum.
2. Cast Poro Snax
3. Enemy casts Death's Hand on Braum, which will deal damage to Braum, triggering a Mighty Poro to summon, and also deal killing damage to the Nexus.

The Mighty Poro might not get the Poro Snax everywhere buff. It depends on if the everywhere buff on the Nexus sees the Mighty Poro summon event before the Nexus is marked for death. TBH it probably does, but I'd have to go look at the code to know for sure and it is Friday night so I'll probably pass on that :)