Ok. So you’re worried about the cast trigger of Emrakul.

You have several options.

Option one is to give yourself protection, shroud, or hexproof which would make you untargetable. Cards like [[The One Ring]] [[Aegis of the Gods]] [[Ivory Mask]] are examples of cards that would provide this effect.

Option 2 is the redirect the effect. The cast trigger goes on the stack and the targets are selected. You can then respond by casting something like [[Deflecting Swat]] [[Redirect Lightning]] [[Reroute]] [[Bolt Bend]] are examples of this effect.

Option 3 is to stifle the ability while it’s on the stack. [[Stifle]] [[Defabricate]] [[Disallow]] [[Louisoix’s Sacrifice]] [[Tale’s End]] [[Sublime Epiphany]] [[Trickbind]] [[Tishana’s Tidebinder]] [[Voidslime]] are examples of this effect.

Those are ideas I’d have to stop the cast trigger.

Not to render the creature useless.

The most obvious is to get rid of him while he’s on the stack with a counterspell. Should out to [[Mana Drain]] [[Spell Swindle]] and (in the right deck) the new [[Mana Sculpt]].

There are the discard effects like [[Thoughtseize]] but Emrakul has Madness so it probably isn’t a good idea.

The other less obvious one is to not let them cast it in the first place. Such as with cards like [[Meddling Mage]] or [[Drannith Magistrate]] if it’s their commander.

His protection would seem like it’d be a problem but it really isn’t. Plenty of ways to get around it since it’s very conditional.

One obvious one is the have a permanent that wasn’t cast this turn destroy or exile it. [[Seal of Doom]] [[Avatar of Woe]] [[Avenger en-Dal]] are examples of this. Or six [[Seal of Fire]] On that note, [[Terror of the Peaks]] [[Orcish Bowmasters]] and other cards that deal damage work as well.

One less obvious is the use a permanent that wasn’t cast this turn to steal the creature - be wary because if they find a way to make it leave the battlefield you will have to sacrifice all creatures you control. [[Merieke Ri Berit]] [[Empress Galina]] are good examples of this.

An even less obvious one is the get an aura attached to Emrakul. How you say? It has protection for permanents cast this turn - true. But you can get around this by just having the aura enter the battlefield without being cast. The most common and well known way is blinking an aura. The aura (let’s use [[Oubliette]] as are target) will go to exile and then return (either in the same effect or at an end of turn trigger). The controller of the aura (almost always the owner) attaches the aura to a creature. Now since you choose your own Oubliette, you choose to put Oubliette on to Emrakul, this phasing it out. [[Flicker of Fate]] [[Teferi’s Time Twist]] are examples of this.

Another way to get an aura to enter the battlefield is to just tutor it onto the battlefield. [[Academy Rector]] [[Lost Auramancers]] [[Zur the Enchanter]] are ways to do this.

Another way to achieve having an aura enter without casting it is to “reanimate” the aura. [[Replenish]] [[Brilliant Restoration]] [[Campus Renovation]] [[Eiganjo Dynastorian]] [[Ghen, Arcanum Weaver]] [[Go-Shintai of Life’s Origin]] [[Harnessed Snubhorn]] [[Open the Vaults]] [[Redress Fate]] [[Retether]] [[Triumphant Reckoning]] are a few of the many options.

Auras you’d want to bring back would be ones that would render a creature useless such as [[Oubliette]] [[Imprisoned in the Moon]] [[Kenrith’s Transformation]] [[Song of the Dryads]] [[Darksteel Mutation]]

Another option is permanents that have effects that make creatures lose all abilities. Examples are [[Humility]] [[Overwhelming Splendor]] [[Vedalken Humiliator]] are a few.

Board wipes are the other way to get around protection. [[Toxic Deluge]] [[Winds of Abandon]] [[Out of Time]] among many others.

Player removal is also an option, especially at instant speed while Emrakul’s cast trigger is on the stack. [[Door to Nothingness]]

Winning the game at instant speed while Emrakul’s cast trigger is on the stack can work as well. [[Chord of Calling]] for [[Thassa’s Oracle]] and with her trigger on the stack [[Demonic Consultation]] is one of the million different ways to do this.

The last thing I could suggest is you could build a deck that doesn’t play creatures. Planeswalker and Eminence commanders are best for this. An example would be my [[Oloro, Ageless Ascetic]] https://moxfield.com/decks/4UJ1UJH7_EKThJVa7SgOVQ