Extremely impressive! Looks great, plays well. I love the whip animation! You fit a ton of features into a Pico-8 Kart -- multiple difficulties, multiple paths, secrets, a variety of enemies, moving platforms, bosses. This looks like it was a ton of work!
My only critique is that I am partial to how deliberate the movement in the original Castlevania is; I don't like that you can move after whipping or control in mid-air after jumping, but those are points of preference and I don't mean for them to be prescriptive.
Otherwise you nailed the look and feel -- I love this!