So according to the one spell slot a turn rule, a player can not use two spell slots in the same turn. The example given in the PHB is that a player can't use a spell slot in both Action and Bonus Action. According the new Sage Advice, if a Reaction is used during your own turn, you must follow the one spell slot per turn rule. But what about when you don't do this? For instance, can you cast Counterspell using a spell slot in your Reaction when during your Action you used a spell slot to cast Fireball?

It's fairly rare for Reactions to occur during your turn. I suppose if you Fireball'd someone, they Absorb'd Elements and then you tried to Counterspell the Absorb Elements, you'd run afoul of the rule. However, in most cases Reactions don't occur on your turn.

Note that the Ready Action still involves casting the spell on your turn (and is thus subject to the one-spell-slot-per-turn rule). It's just the final release of the spell that's delayed.

Quote from AelenSagegazerDnD >>

So according to the one spell slot a turn rule, a player can not use two spell slots in the same turn. The example given in the PHB is that a player can't use a spell slot in both Action and Bonus Action. According the new Sage Advice, if a Reaction is used during your own turn, you must follow the one spell slot per turn rule. But what about when you don't do this? For instance, can you cast Counterspell using a spell slot in your Reaction when during your Action you used a spell slot to cast Fireball?

If you use your Reaction on your turn (which is relatively rare, but does happen) then it counts as being on your turn. So no, you can't use a spell slot to cast Counterspell on the same turn that you used a spell slot to cast Fireball.

Yes, as long as it isn't on your turn.

Just for future reference, this is the answer from the SAC:

Can you cast a Reaction spell on your turn?
Yes, but you must abide by the rule of expending only one spell slot to cast a spell on your turn. For example, if you take a Magic action to cast Fireball using a spell slot and an enemy casts Counterspell, you can’t also then expend a spell slot to cast Counterspell targeting that enemy.

Also, as a suggestion for the OP, you could cast more than one leveled spell using your Magic Action, Bonus Action, and/or Reaction on your turn if those spells come from traits/features/feats that let characters cast them without using a spell slot, or from magic items. For example, a Spell Scroll of Counterspell for this scenario.

Quote from AelenSagegazerDnD >>

So according to the one spell slot a turn rule, a player can not use two spell slots in the same turn. The example given in the PHB is that a player can't use a spell slot in both Action and Bonus Action. According the new Sage Advice, if a Reaction is used during your own turn, you must follow the one spell slot per turn rule. But what about when you don't do this? For instance, can you cast Counterspell using a spell slot in your Reaction when during your Action you used a spell slot to cast Fireball?

This is perfectly acceptable.

Just remember that in this game any feature or effect that occurs or is restricted to "once per turn" does not actually mean once per round, nor does it mean once per turn only on your own turn.  "Once per turn" means once per anyone's turn.  So, you can cast one spell with a spell slot on your turn.  Then, as soon as it becomes someone else's turn you can again cast one spell with a spell slot on that turn, and then as soon as it becomes a third creature's turn you can again cast one spell with a spell slot on that turn, and so on.

Quote from up2ng >>

Quote from AelenSagegazerDnD >>

So according to the one spell slot a turn rule, a player can not use two spell slots in the same turn. The example given in the PHB is that a player can't use a spell slot in both Action and Bonus Action. According the new Sage Advice, if a Reaction is used during your own turn, you must follow the one spell slot per turn rule. But what about when you don't do this? For instance, can you cast Counterspell using a spell slot in your Reaction when during your Action you used a spell slot to cast Fireball?

 

This is perfectly acceptable.

Just remember that in this game any feature or effect that occurs or is restricted to "once per turn" does not actually mean once per round, nor does it mean once per turn only on your own turn.  "Once per turn" means once per anyone's turn.  So, you can cast one spell with a spell slot on your turn.  Then, as soon as it becomes someone else's turn you can again cast one spell with a spell slot on that turn, and then as soon as it becomes a third creature's turn you can again cast one spell with a spell slot on that turn, and so on.

 this is incorrect. other wise double sneak attack would not work .and it does they even have a feat for it.

other wise double sneak attack ... have a feat for it.

Can you explain what a double sneak attack is and what feat that allows it?  I can't search & find double sneak attack.

Zhentarim Tactics when used on a rogue allows you to retaliate if you get attacked, if you are able to maintain a way to keep advantage on the enemy while they attack you

you can sneak attack twice.

Quote from Character77006 >>

other wise double sneak attack ... have a feat for it.

Can you explain what a double sneak attack is and what feat that allows it?  I can't search & find double sneak attack.

I am not aware of a way to get two sneak attacks in one turn. I am fairly confident Nightmorph is wrong.

You can get one and only one sneak attack on your turn, but as long as you can attack (or be forced to make an attack) when it is not your turn, you get additional sneak attacks in as long as the attack meets the sneak attack requirements, up to once per turn (as up2ng described). There is no theoretical limit on the number of sneak attacks you can make in one round. The only potential feat that I am aware of that could help is the Unearthed Arcana (Playtest - not officially released) feat, tunnel fighter, which lets you make opportunity attacks without expending your reaction. Tunnel Fighter should not be used at most tables as it is not official and significantly unbalanced.

Zhentarim Tactics 

What is that?  Is that the feat or is it the book a double sneak is from?   

Quote from Character77006 >>

Zhentarim Tactics 

 

What is that?  Is that the feat or is it the book a double sneak is from?   

Zhentarim Tactics is a feat from Heroes of Faerun. It allows making an opportunity attack against a creature as a Reaction when they hit you with a melee attack. It does not allow you to use Sneak Attack twice in the same turn, but it does potentially allow you to use Sneak Attack on someone else's turn. This could allow you to use it twice in the same round (though still not twice on the same turn).

"Double Sneak Attack" is not a thing from a book. It's a misunderstanding Nightmorph seems to have about how Sneak Attack and Zhentarim Tactics work.

Can a Rogue use Sneak Attack more than once per round?
The Sneak Attack description specifies that you can use the feature once per turn, but it’s not limited to your turn. The feature also doesn’t limit the number of times you can use it in a round.

You sometimes get a chance to use Sneak Attack on someone else’s turn. The most common way for this to happen is when an enemy provokes an Opportunity Attack from you. If the requirements for Sneak Attack are met, your Opportunity Attack can benefit from that feature.

Quote from Tarod_ >>

Can a Rogue use Sneak Attack more than once per round?
The Sneak Attack description specifies that you can use the feature once per turn, but it’s not limited to your turn. The feature also doesn’t limit the number of times you can use it in a round.

You sometimes get a chance to use Sneak Attack on someone else’s turn. The most common way for this to happen is when an enemy provokes an Opportunity Attack from you. If the requirements for Sneak Attack are met, your Opportunity Attack can benefit from that feature.

 100 percent.

ok I may not have phrased it the best, but what I said was correct you can get sneak attack twice if you fulfill the conditions .

Quote from wagnarokkr >>

Quote from Character77006 >>

Zhentarim Tactics 

 

What is that?  Is that the feat or is it the book a double sneak is from?   

Zhentarim Tactics is a feat from Heroes of Faerun. It allows making an opportunity attack against a creature as a Reaction when they hit you with a melee attack. It does not allow you to use Sneak Attack twice in the same turn, but it does potentially allow you to use Sneak Attack on someone else's turn. This could allow you to use it twice in the same round (though still not twice on the same turn).

"Double Sneak Attack" is not a thing from a book. It's a misunderstanding Nightmorph seems to have about how Sneak Attack and Zhentarim Tactics work.

 

I never said once per turn on this one I was correcting him saying once per equals any ones turn which would be part of the round so in this case I am right and you misunderstood me . ill grant ya i could have used better verbiage. 

Quote from Nightmorph >>

Quote from up2ng >>

Quote from AelenSagegazerDnD >>

So according to the one spell slot a turn rule, a player can not use two spell slots in the same turn. The example given in the PHB is that a player can't use a spell slot in both Action and Bonus Action. According the new Sage Advice, if a Reaction is used during your own turn, you must follow the one spell slot per turn rule. But what about when you don't do this? For instance, can you cast Counterspell using a spell slot in your Reaction when during your Action you used a spell slot to cast Fireball?

 

This is perfectly acceptable.

Just remember that in this game any feature or effect that occurs or is restricted to "once per turn" does not actually mean once per round, nor does it mean once per turn only on your own turn.  "Once per turn" means once per anyone's turn.  So, you can cast one spell with a spell slot on your turn.  Then, as soon as it becomes someone else's turn you can again cast one spell with a spell slot on that turn, and then as soon as it becomes a third creature's turn you can again cast one spell with a spell slot on that turn, and so on.

 this is incorrect. other wise double sneak attack would not work .and it does they even have a feat for it.

The above description of the mechanic is 100% correct.  It's not helpful to resurrect an old thread to make an inaccurate claim like this.

Quote from SmiteMakesRight_3_5 >>

Quote from Character77006 >>

other wise double sneak attack ... have a feat for it.

Can you explain what a double sneak attack is and what feat that allows it?  I can't search & find double sneak attack.

I am not aware of a way to get two sneak attacks in one turn. I am fairly confident Nightmorph is wrong.

There is a way, actually, the 17th level feature for the Scout Subclass (XGtE).

Sudden Strike

Starting at 17th level, you can strike with deadly speed. If you take the Attack action on your turn, you can make one additional attack as a bonus action. This attack can benefit from your Sneak Attack even if you have already used it this turn, but you can’t use your Sneak Attack against the same target more than once in a turn.

But not a lot of Rogues will see 17th level, let alone with the Scout subclass.

Quote from up2ng >>

Quote from Nightmorph >>

Quote from up2ng >>

Quote from AelenSagegazerDnD >>

So according to the one spell slot a turn rule, a player can not use two spell slots in the same turn. The example given in the PHB is that a player can't use a spell slot in both Action and Bonus Action. According the new Sage Advice, if a Reaction is used during your own turn, you must follow the one spell slot per turn rule. But what about when you don't do this? For instance, can you cast Counterspell using a spell slot in your Reaction when during your Action you used a spell slot to cast Fireball?

 

This is perfectly acceptable.

Just remember that in this game any feature or effect that occurs or is restricted to "once per turn" does not actually mean once per round, nor does it mean once per turn only on your own turn.  "Once per turn" means once per anyone's turn.  So, you can cast one spell with a spell slot on your turn.  Then, as soon as it becomes someone else's turn you can again cast one spell with a spell slot on that turn, and then as soon as it becomes a third creature's turn you can again cast one spell with a spell slot on that turn, and so on.

 this is incorrect. other wise double sneak attack would not work .and it does they even have a feat for it.

 

The above description of the mechanic is 100% correct.  It's not helpful to resurrect an old thread to make an inaccurate claim like this.

 I know your trying to troll me but I'll take the bait. what i said was correct what you said was incorrect .once per turn does not mean once per anyone's turn otherwise they would say once per round. its ok to be wrong .