the new eldritch strike and war magic sync

Im DMing a vecna eve of ruin campaign at the moment and have a EK player at the table and we had a little discussion about the use of ES and WM traits 
According to him how he reads the traits he should be able to make 2 attacks and cast a cantrip at level 11 which in my eyes seems fine if it was not for the ES that he wanted to use like twice 

example: Attack that procs ES, cantrip in this case mind sliver that uses the ES debuff, then another attack where he wants another ES debuff on the monster.

Is this a legit thing he could do or not 

sorry in advance for my bad sentence structure

At level 11, a Figther can attack three times instead of once whenever they take the Attack action on their turn. Thanks to the Level 7: War Magic feature, you can replace one of the attacks with a casting of one of your Wizard cantrips that has a casting time of an action. In your exaple, the second attack is replaced by the Mind Sliver. That works fine.

And I'd say Level 10: Eldritch Strike is (re)applied every time you hit a creature with a weapon attack, so your example looks legit to me.

But I don't see how the last attack that applies Disadvantage on the next saving throw is useful, if the Figther is not casting a new spell before the end of their next turn.

EDIT: for clarity.

okay thanks for the reply 

at the end of your next turn is when the iniative is gone through completly and the fighter is next so than he can do the same thing again right or he attacks 3times or he uses a better spell that might need a saving throw like lets  rime's binding ice or am i wrong in what they mean with next turn 

yes thats what i mean thanks for the help both of you 

Quote from TarodNet >>

 

But I don't see how the last attack that applies Disadvantage on the next saving throw is useful, if the Figther is not casting a new spell before the end of their next turn.

There are two useful scenarios for this, 1st is action surge. As War Magic is per Attack Action, you can use it twice in 1 turn with Action Surge. Technically you can use it up to three times with Haste... 

the 2nd scenario is that you plan to not use an attack action on the next turn. Perhaps you plan to use an AoE or some other type of spell, you could hit three creatures in round 1 then in round 2, if they don't move away you can thunder wave them all making the saves a lot more difficult. More so a tactic that could be used some where near a cliff or pit... somewhere to help inflict extra fall damage and prone.

Quote from R3sistance >>

Quote from TarodNet >>

 

But I don't see how the last attack that applies Disadvantage on the next saving throw is useful, if the Figther is not casting a new spell before the end of their next turn.

There are two useful scenarios for this, 1st is action surge. As War Magic is per Attack Action, you can use it twice in 1 turn with Action Surge. Technically you can use it up to three times with Haste... 

the 2nd scenario is that you plan to not use an attack action on the next turn. Perhaps you plan to use an AoE or some other type of spell, you could hit three creatures in round 1 then in round 2, if they don't move away you can thunder wave them all making the saves a lot more difficult. More so a tactic that could be used some where near a cliff or pit... somewhere to help inflict extra fall damage and prone.

 Totally. Thanks R3sistance! Very useful (and deadly) scenarios.

Frankly, I just highlighted that to make Bunny aware the last attack (if it hits) is useful depending on your next actions.