The first video of the final boss Battle with Bowser has surfaced. It looks like the main objective is to throw dice blocks at Bowser. You have to flip the dice over to face your head on top instead of Bowser’s. Every dice that has your head on it by the time the 10 second timer ends, you get a point and cause damage to During Bowser’s 2nd phase, he sends a lot of bosses such as King Bob-omb, Boo, and Chain Chomp (as seen in the NA commercial) in the middle of the arena to harass you. He also tilts the stage when then dice blocks come to make it harder to flip them.
Spike is the mini-boss for Magma Mines. His boss battle is a reflex type game. As Spike rolls spiky balls at you, you have to hit them back at him with hammers. On the screen 5 random objects appear. Usually there is at least one gold hammer, normal hammer, and twig. The twig does nothing and makes you lose a point, the hammer gives you a point, and the golden hammer gives you 3 points. His 2nd phase involves the time between picking the objects that appear on the screen to the time the spikes getting faster as the lava behind the characters gets shortened.
Thanks to TheBitBlock for the videos
UPDATE: Also, here is the ending cinematic after you defeat Bowser.