One of the things that make Atsushi great over ok is having a way to ensure Atsushi dies on your terms - and blitz does just that
You get evasion, all damage prevented to your attackers, and a massive, indestructible beater to apply pressure
The concepts are fun to speculate about, but I honestly can't see a nonbroken sword that gives protection from creatures or players making it to actual print
I think Endless One could be fine in a deck that has a focus on the +1/+1 counters on your creatures with cards like Avatar of the Resolute, but as a big payoff spell, the other options are miles better
If another effect allows you to play a card for a different alternative cost, including "without paying its mana cost," you can't also choose to pay its web-slinging cost
Try to use Terra and other cards like Gogo: Mysterious Mine, which can become a copy of Terra to quickly get his cost down by adding creatures to the graveyard