Play as the Falconess:
To gain the secret character 'The Falconess', who uses the same turbo attacks as the valkyrie, go to the Bonus Stage in the Castle World. Get 50 of the coins there. This will nake 'The Falconess' avalibale for you to use at any time!

Play as the Jackal:
You will have to go to the first town level of the Ice World. At the end on top of the pile of crates, there is a trapdoor at a dead end. The trapdoor is found by climbing the slanted crates to the top, then circle around until you get a chance to go back down. From there, climb the other set of slanted crates, located before the exit, and standing atop of the trapdoor. Inside the door collect 50 coins, before your precious time runs out and you will gain 'The Jackal.'