when you say that stax is a good matchup, did you test Uba Stax?
REB's will be dead cards, vial and jitte get shut off by rod, chalice can be eaten by shaman (if they even need to), waste/strip will be a pain with only 2 basic lands, and the hate outta the board (Rack and Ruin) is horrible vs Uba Mask.
In this match-up I feel like the Ninja's and voidmages may be too slow, but at least the grim's and hatchlings could be a pain.
Not really, it's not like Uba Stax has been widely played at all so I never bothered testing it until like a week ago. It's certainly a worse match than other Stax decks, but it's not quite as god-awful as you make it sound. In the match there are 3 cards I hate seeing. Null Rod, Smokestack and Trinisphere. Uba Mask seems painful, but it really isn't. Most of the build is permenants. Only 1/5th of the deck is actually affected and the majority of the time those counters are shitty topdecks anyway. Crucible Strip is bad, but that's awful to play against with every deck. I originally had 4 Island's maindeck until I realized I consistently only need 1-2 Island in play to begin with. So it's worse, but I don't know exactly how much so.
I'm mentally comparing this list to WTF and I can't figure out where it gains any advantage.
Ninja: I never found Ninja doing much for me because the games were over too quickly; either Mongrel + Jitte came in for the win or they Giftsed and won. Also, it's situationally dead, and sucks up a lot of mana. The change that was strongly recommended to me by #TMD was Roowater Thief. This would help shore up a lot of bad matchups, especially Oath. He also makes Jitte worse by a little.
Voidmage Prodigy: I'd think this would rack up the deck's weakness to cards like Fire/Ice and Lava Dart by increasing the number of dudes you run with a butt of 1. Also, with the Ninjas and the Jittes, how often are you going to be having the mana to counter stuff with this?
Draw: I know, you say Ninja + Ancestral is enough, but it isn't. With Fish scrubbing out of SCG, everyone thinks it sucks, so it's a good time to run Standstill again. Although you could get away with running Brainstorm since you care about specific cards like Jitte more than you just need a bunch of cards to feed a hungry Mongrel.
Sideboard: I'd recommend 2x Rushing River. Not only does it help against Oath but it's an option against Gifts, especially with many of the Gifts players being unable to Tendrils unless you hand it to them. I'd also get the 4th Jitte, just because in many matchups you're going to rely on pulling Jitte and winning (like Shop decks, or Goblins).
No Kira, by the way? Not only does it help you where you expect Old Man (like Stax), but where it's relevant you have an extra creature to swing with, and she hits for two in the air. You only have one other flier, and that's Spiketail.
It gains a major advantage in the CS and Gifts matches by having more mana disruption and more counters. WTF focuses way more on beating down than disrupting and that just kills it sometimes.
Ninja is draw. Shitty draw, but draw none the less. He's also a creature which is valuable when you choose to cut the asstatic factories.
Voidmage: I consistently have mana to power him if I choose. The entire deck is a careful balance of give and take. You want to play out threats on a semi-consistent basis, but hold back to deter the opponent from trying to resolve anything good. It's more of a instinct thing.
Standstill is awful. That's where I stand on it. When I usually wanted to cast it, it left me tapped out more often than not. Many times I wished I rather had a threat or counter in it's place. Other times it'd be on the board, but I couldn't coax my opponent into actviating it until he was damn well ready. Meanwhile I sat there looking like a chump unable to play more threats or Jitte.
Kira is a decent choice for the board. In the maindeck she's worthless. Nobody plays maindeck spot removal anymore and she costs 3 which is just bullshit period. Why Rushing River over Echoing Truth or Chain of Vapor though? Is it just to bounce Oath and a creature togheter?