Alrighty, I've opted to do this week's card discussion, so this time we'll be talking about Vanity's Emptiness.
Its relevance is obvious, considering it sees play in many competitive decks nowadays. But what are its implications for play?
First, it's important to know exactly what it does and does not do. Looking at its effect text:
"Neither player can Special Summon monsters. When a card is sent from the Deck or the field to your Graveyard: Destroy this card."
This tells us a few things. Now that the card has been updated with PSCT, it's easier to see that its effect to destroy itself does start a chain. This means that you don't just destroy Vanity's Emptiness immediately after a card is sent from the Deck or field to your Graveyard; you put its effect on a new chain and resolve accordingly. Also, it doesn't actually negate or destroy anything. If I activate the effect of Rubic, Malebranche of the Burning Abyss in my hand and my opponent chains Vanity's Emptiness, and that chain resolves, Rubic just stays in my hand instead of going to the Graveyard or anywhere else.
The effect to destroy itself is mandatory, but is just that: an effect. Trap Stun will still negate that effect, for example, even though it won't prevent the activation.
Also, you can't just flip it face-up while your opponent is conducting a Special Summon off of the chain. If my opponent attempts to Special Summon Cyber Dragon by its own effect from the hand, I can't just activate Vanity's Emptiness to keep it in the hand. My opponent on their own turn has the right to act first in an open game state, and Vanity's Emptiness can't interrupt the progression of an already-attempted Special Summon that happens off of the chain.
As an aside, Vanity's Emptiness will only prevent optional effects that mandatorily Special Summon from activating. So if Vanity's Emptiness is applying its effect, you can't activate the effect of Ghostrick Jackfrost in the hand, nor can you activate either activated effect of Cir, Malebranche of the Burning Abyss; you can and must activate the effect of a banished Angel of Zera if its trigger is met, even if Vanity's Emptiness is applying, and assuming the absence of other effects, the effect of Angel of Zera will resolve without effect. You may also activate the effect of Fire Hand or Ice Hand, since they optionally Special Summon, and you may activate Macro Cosmos (since it also optionally Special Summons on its initial activation as opposed to mandatorily Special Summoning).
Here's an example of a slightly more complicated situation than the ones I discuss above: My opponent's Thunder King Rai-Oh has its effects negated by Breakthrough Skill. I attempt to Special Summon Dark Armed Dragon, my opponent for some reason tries to negate its Special Summon with Thunder King Rai-Oh, but then activates Call of the Haunted targeting their Thunder King after I confirm I have no response to Thunder King's effect activation; I chain Vanity's Emptiness and the chain resolves backwards, resulting in Vanity's Emptiness applying its effect, Call of the Haunted resolving without effect since monsters can't be Special Summoned (it stays face-up on the field as an effectively dead card), Thunder King Rai-Oh's effect being negated, and Dark Armed Dragon being Special Summoned successfully (since again, the Special Summon off of the chain has already been attempted; Vanity's Emptiness cannot prevent this one even though it's resolved before the Special Summon is successful).
Obscure interactions aside, the card is quite relevant in competitive play, and you will be expected to either play it, or know how to beat it, in order to consistently win if your Deck is in any way reliant on Special Summoning. Feel free to ask any questions you may have about the card or its interactions in the comments, and discuss!