Mega Man X/Flame Mammoth
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Now that you've defeated Chill Penguin (you have haven't you?!) Flame Mammoth's level will be significantly easier. After defeating Chill Penguin Flame Mammoth's stage gets frozen over. All the pits of lava no longer exist and so you can cruise through this stage faster than any other.
You'll be able to get both the Heart Tank of this level and the Sub Tank if you have beeaten Chill Penguin.