[No where in the video dose he say he was going to deport 800,000 Dreamers]
No one claimed that he did, so I don't understand why you requested such a citation.  Is that supposed to be a straw man argument?
[He said he was ending the DACA program for future Dreamers]
No.  He said he promised to end the DACA program meaning he was going to remove the protection DACA provided to all, not just future but ALL DACA recipients.
[To consider if Trump's action to end DACA was "legal" it would need to be proven that DACA was legal in the first place]
Exactly how do you come to that conclusion?  There is no 'case or controversy' as it no longer legally exists.  Or as I put it previously, the issue is not moot.
[If ending DACA puts Congress's feet to the fire ]
Has absolutely no bearing on Trump's choices or actions most notably those he made before becoming President.