make like a "timer" to push the a block blocking the moving block to pass, rotating the other moving block to left and pushing the blocking block, like...
18 by 3 map:
M = moving blocks
R = rotating blocks
B = barrel block
|--------M-------R-|
|--------B-------M-|
understand? the right is the timer to unlock the passage, then the first moving block will pass and kill the enemy, the rotating block function is to rotate the second moving block to move to the left direction.