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When you get to the section where there's a green ice block above you (one bound to move) and a silver ramp leading diagonally down to the right, simply run and dash down it. When you get to the bottom wall jump upwards before you get crushed by the block! Run forwards, slide down the left wall and head through the small tunnel past 3 wall clinging enemies to reach the head armor upgrade. Get it, get the extra life if you like, run back to the big gap, dash jump to the other side and wall climb to safety. Follow the ramp to the upper right (ignore the ladder), kill the 3 bats, then approach the green ice block. It will unhinge as usual, so run back to safety. You can either climb the ladder slightly, or just stand to the left of the small indentation below the ladder (it fits nicely right there).