The single clearest thing anyone has said about Project Rabbit comes from the developer, and it is worth putting first: "Extraction is Secondary, the Core is Soulslike." Everything else in the game hangs off the combat.
The combat vocabulary is Sekiro's, and it is explicitly not a new one. From the PlayX4 build and the trailers, four actions carry the fight:
On top of the four sits a layer of active combat skills, which the developers describe as "diverse" without enumerating them. The store copy's warning is the important part operationally: "even the smallest mistake can lead to a fatal conclusion". In a game where a fatal conclusion means losing everything, that sentence is the whole difficulty design in one line.
The on-site PlayX4 impression of "90% familiar, 10% unfamiliar" is the useful framing for what to expect. The familiar part is the parry rhythm. The unfamiliar part is that you are not fighting through a designed level sequence — you are fighting through a randomised one, and every attempt can end with you walking out poor rather than dead.
Three categories have been shown, and none of them have official names yet.
What is not shown is a roster of named bosses. The November 10 trailer contains a first look at a new boss that is never named on screen, and it has a distinctly East Asian mythological silhouette — a large figure with horns or a headdress — but the studio has not attached a name to it. The same applies to the "Mad Hatter", "Cheshire Cat", "Red Queen" and "March Hare" figures: they are confirmed characters with dark secrets behind them, per the official copy, but the game has not yet told us what those secrets are.
Bosses in Project Rabbit are confirmed to have multiple phases that require you to change your tactics mid-fight. That is a specific design commitment: not a health bar with escalating damage, but a fight that stops working the way you had it working. If you learn a rhythm, the game is expected to invalidate it partway through.
The practical consequence for group play is that multi-phase bosses are where co-op coordination and solo fragility diverge most sharply. Several outlets raised this as a risk: a co-op team can adjust, split aggro and cover each other's recovery windows, while a solo player facing a phase change has nobody to buy time. If you are planning to play this solo when it launches, the boss roster is the page to watch when the names arrive.