Ok, this cards is one of the most underrated card for me, and also the card i love the most in the entire game.
This beauty took me a lot of time to fully understand it, and you'll need a really good understanding of how the stack work to play it properly.
You'll make a lot of mistakes with it even after 200+ games with this deck.
First, let me give you a list of the cards you'll use the effect for most of the time : Glimmerpoint Stag, Flickerwisp, Spell Queller, Ideas Unbound, Turn to Mist, Detention Sphere, Voyager Staff and Mimic Vat.
But don't forget that it is useful on almost each of your turns with almost all of your cards.
You'll always want to have a sundial on your board, even just to put your opponent in a threat situation where he'll use tons of cards just to get rid of this artefact.
Now let me show you an example of one (complicated) of the hundreds situations you can use it properly:
First let's say your mana pool is infinite.
It is your turn.
You first play Soulherder.
Your opponent counter it with a Counterspell.
In response to negate, you cast a Spell Queller targeting the Counterspell.
The stack resolve.
You play a Sundial of the Infinite.
Now you play a Flickerwisp and exile one of the lands of the the opponent.
You arrive at the core moment : the beginning of the end step.
It's your turn so you decide the order on the stack of all the triggers who arrived at the same moment.
So you choose to first put the return on the land first, then the Soulherder.
So the first effect to trigger is the one of the Soulherder (stack always begin to resolve with the last spell).
You use it on the spell queller.
So 3 effects are now on the stack, first the land who is supposed to return, then the "leave the battlefield" effect of the spell queller, and finally the "enter the battlefield" of the spell queller.
You let the "enter" effect triggers on nothing (yeepee), and then you use the Sundial of the Infinite ability.
The stack is exiled and the "leave the battlefield" effect (who is suppose to let the opponent play his Counterspell for free) and the return of the land are exile forever.
Hope this little example helps you to better understand the Sundial of the Infinite.
Don't forget that it had tons and tons of other abilities.
Keep in mind too that if you use it before your end step, all the effets that say "at the beginning of the next end step" will trigger at the beginning of the opponent's end steps, which can still be useful in certain situations.
