I have been thinking about this card lately, and whether it exceeds my DFC threshold. The first two chapters are pretty much whatever, but I like that it introduces the same pattern as The Mirari Conjecture, by going "In two turns, you will have to leverage this card for something exciting." However, it would also be very easy to make a proxy of it that just makes a token, but at the same time, changing the functionality of existing cards isn't really a can of worms I want to open up in the cube.
edit: wait, I was certain this stupid card triggered on etb, not on being blocked. Nevermind, I've lost interest.
The other thing I've been considering lately is ninjas. I think ninjutsu adds a lot of interesting interactions both in terms of card synergy and to decision making in a game of magic, but I don't like how much a lot of the existing ninjas are basically one-shot spells that are sitting ducks after they do their one trick.
Prosperous Thief gets around this issue by making all your rogues and ninjas into saboteurs. I don't believe I have the necessary density to make this card appealing on those grounds, but with some effort I could see it having some worth.
Thousand-Faced Shadows sort of solves the ninja issue by actually not being a saboteur, it is actually a glorified spell that still encourages creatures that are evasive or have useful etb-effects. Also you can tutor for it with white rangers.
The last two I'm undecided on, they're not all that interesting to me, so it mostly comes down to "How badly do I want ninjas?" They have a solid enough floor that doesn't make you sad about not being able to turn them on, and the isolated decision-making the card provides is interesting, but they both rely on ninjutsu being inherently interesting enough for me to want to include them. I suppose they have synergy with blink-effects and I guess proliferate.
I think what I was hoping for was something along the lines of:
Creature - Rat Ninja
Sacrifice a creature: ~ gains menace until end of turn.
Whenever ~ deals combat damage to a player, return target creature card in your graveyard to your hand.
which, rough sketch, but I could see pairing with aristocrats, etb creatures, or evasion pieces.
so tl;dr: Probably adding Thousand-Faced Shadows, and maybe adding the ninja turtle or palm guy.