It is a replacement effect and not a triggered ability, therefore it would do its thing before the action actually happens, in this case triggering something's ETB effect.
My interpretation : Since it says "If an artifact or creature entering the battlefield causes a triggered ability of a permanent you control to trigger, that ability triggers an additional time." and the permanent's own ability would cause an ability to trigger, it should double it. It is a replacement effect, it doesn't need to trigger off a triggered ability like Strionic Resonator would.
Keeping track of which creatures created which emblems, as well as what to do with emblems sitting around after the creatures that created them are removed (by removal or combat) or the counters are depleted, would be a hassle and a lot of extra space used that really isn't in a normally used zone. First, a mechanic that can interact with emblems in the first place would needed, then something like this mechanic, but not as it is presented here now, could become a thing. Tying an emblem in one zone to a creature in another zone is bad design, as "bookkeeping" is a nightmare, especially if clone effects are used.
Sacrificing the creatures is a cost paid when activating the ability, not upon resolution of the ability, therefore you cannot destroy one before he has already sacrificed it from paying the cost to activate the ability. Pretty much anything he does BEFORE the : sign is done before anyone can do anything else.
It is really sounding a lot like the Chain Veil influencing things. Whispers, buzzing, corruption, a desire to wipe out everything - all very Onakke. We know Liliana brought the Chain Veil here, as she is the poster child for the second set. We also all know that no matter the purity of the those who run into its power, the Chain Veil can corrupt them with its dark mana. Look at poor Garruk, Apex Predator. Look at the countless angels Liliana has vaporized with its power. The only other plausible source of this madness is Nicol Bolas, Planeswalker.
That way it constitutes a part of (magic) physical nature whereupon mana can be drawn, i.e. the space between planes, like outer space is to us in the real world. It also ties in not only colorless magic, as it is the magic of the blind eternities, but also gives a "home land" to the Eldrazi.
But how fun is this and Mikaeus, the Unhallowed? Seriously makes for double undying on your guys and paired with Cauldron of Souls it can be a super fun strategy.
Bolas could very well want to use a method like powerstones, as it would allow him constant access to the Eldrazi for research and power-siphoning. Imagine Bolas slinging "pokeball" powerstones around containing Eldrazi!
Liliana is a premending Dominarian walker, and a talented necromancer, so there is a chance she could be persuaded find someone on Dominaria, dead or living, and get the information. As much as it pains me to say, Jace could manipulate her into doing it for him. Phthesis was caused by continuous and extreme exposure to powerstones, as none of Urza's men experienced it when they were working with and around the powerstones he excavated and used in the Brothers' War. And Urza was immune to it while having a powerstone as his eyes, so Ugin may be immune as well.
If I recall correctly, Dominarian powerstones could be used to harness great deals of mana, going so far as to absorb the collapsed plane of Serra's Realm. So, would it be possible to find and repair the old Mana Rig on Dominaria, create a massive powerstone, charge it with a collapsing plane, and use it to lure the Eldrazi to it and create a better, smaller, and more humane Eldrazi-trap? Ugin could even carry it around as a necklace if he wanted to, in order to better protect it.
I may be mistaken, but I do believe Dyfed was able to planeswalk into a powerstone to prove it can contain a plane itself, so I do not believe this idea is unreasonable.
Honestly, standard needs to be toned down and cards need to be nerfed. Power creep has gotten way out of control over the last 10 years, and I'm very happy that they are reigning it in. Standard is a format by design to force players to be innovative with their available pool to make viable decks, not to play modern-lite or legacy-lite. If you can't afford to play in an eternal format, then you play standard, but don't expect to have access to the power of an eternal format in a limited-risk limited-investment format. I feel like too many people are getting comfortable with netdecking instead of innovating for themselves, and that is why they are frustrated with newer cards being "weaker" than older ones, since these new ones require working with them in order to make a good deck, instead of just inserting a new card that fills the role of a rotated one.
Mikaeus, the Unhallowed has won me tournaments as my artifact commander. His undying with +1/+1 counter creatures is insane, and offset his passive +1/+1 with Heartless Summoning to get free guys out. Excellent tutors, Dark Ritual, Culling the Weak, etc....I've turn 1 Karn Liberated before. I've also won turn 4 upkeep with Darksteel Reactor because of Coretapper, Power Conduit, and Dross Scorpion with Mike out. Monoblack artifacts definitely works and works very well.
Hello Wastes, you look familiar
I do believe Kozilek is in the core area, much like how Mirrodin has a hollow core area, and is feeding/spawning there.
I may be mistaken, but I do believe Dyfed was able to planeswalk into a powerstone to prove it can contain a plane itself, so I do not believe this idea is unreasonable.