When you reach the end of Level 1, you will meet Arma, a laughing gargoyle with feathery wings. Beat him for the Earth Crest. It will allow Firebrand to change into the Ground Gargoyle, which can destroy and move certain stage objects, like statues. This one is mandatory.

When you get to the part of Level 4 where you're flying through the air, near the end you'll notice a greenish whirlwind going down off the bottom of the screen. Fall into it to find the tower that's covered in plants.

    

Ascend all the way to the top of the plant tower and exit through the top right door. Keep going across the bridge with the full moon in the background and you'll find Arma again. Beat him for the Air Crest. This will allow Firebrand to change into the Aerial Gargoyle, which can fly upwards.

    

Go to Level 5 and follow the main (dry) path through the temple all the way to the end. You'll fight a slimy boss called the Crawler. Beat the Crawler for the Water Crest. The Water Crest will allow Firebrand to turn into the Tidal Gargoyle, which can swim freely underwater without taking damage.

    

Go to Level 6 and take the upper path from the first area. (Use the Aerial Gargoyle to reach the entranceway that's hidden in the sky.) Follow this path through the ice caverns and beat the Flier rematch boss fight. Keep going past him, through more ice caverns, all the way to the end. You'll find Arma for a third and final time. Beat him for the Time Crest. This allows Firebrand to transform into the Legendary Gargoyle, which has a doubled HP meter.

    

When you have all the items in the game except for the final crest, go to Level 7 and head all the way to the end. Beat the boss, Phalanx and he'll relinquish the Crest of Heaven. However, you can't get it just yet. Instead, Phalanx will transform into a giant green snake-like demon sticking out of a pool of lava. Beat this form to end the game and see an ending sequence. At the very end, you'll be given a password. Reset the game and continue with this password.

    

Check your subscreen and you'll see that you now have the Crest of Heaven, which grants Firebrand the Ultimate Gargoyle form. This form has all the abilities of the other forms combined. It can break statues like the Ground Gargoyle, fly upwards like the Aerial Gargoyle, swim without taking damage like the Tidal Gargoyle, and has double life power like the Legendary Gargoyle. It also has a pretty strong fire attack and can headbutt like Firebrand's normal form.

    

The Ultimate Gargoyle will also give you access to a bonus final boss - the Dark Demon. Beat him for one more special ending.