I don't know too much about ninjas, I just recently brewed a
ninja deck and I'm still working around it, but I've learnt some things.
I am however experienced with mill since it's one of the archetypes I've played with the most.
First I need to know the budget. Since I see this costs around 108€-179$ I'll move around that. No, I won't be suggesting fetchlands nor stupidly expensive cards.
One of the first things I see is that you're pretty much trying to play a million different creatures and not really commiting to anything specific.
If you wanna mill and play ninjas there are cards that allow that.
Soaring-Thought Thief and
Thieves' Guild Enforcer are good options for that, which also leads you towards a creature type.
Playing with rogues and ninjas is more viable thanks to Kamigawa Neon Dynasty, with cards like
Silver-Fur Master or
Prosperous Thief.
Silver-Fur Master enables Ninjutsu tempo and
Satoru Umezawa, also serving as a lord, while
Prosperous Thief helps ramping.
also in terms of creatures you can easily get rid of the
Slither Blade and the
Mist-Cloaked Herald for a playset of
Thousand-Faced Shadow.
What I mean is that should commit into having more copies of an effective card rather than trying to fit everything into the deck. It's okay if something doesn't fit.
Now that I said my part with ninjas I can go on with mill.
There are two ways it works, either you go all-or-nothing with mill or the control route. Mixing ninjas and mill is doable, you just gotta find a good payoff for using both strategies aside.
I can continue if you'd like, since I can go on for a while