Two Question

1. A simple question: When my oppenent special summons a monster from the extra deck (fusion, synchro or xyz) and I negate the summon, could he later specialsummon that monster again from the grave with Reborn or other cards?

2. About Armored Ninjutsu Art: Rust Mist: Goes this effect only by the first summon/s or also later summons...maybe next turn. I mean when the oppenent special summons again after activation of the trap, will those monsters atk also be halfed?

1. You cann't negate fusion monster summon, ever and never
http://forum.duelingnetwork.com/t4215-an-effect-solemn-warning-ruling-you-might-not-know

Also for fusion additional note:

Spoiler:

2. Same as previous posters answers above, post its card text again here

2.
According to the wording on wikia it should work the same as the anime, halving every monsters attack which is special summoned.

Thanks for the answers. Thread can now be closed/solved.