(C,6)(suicide) Don’t be too hasty!
(D,5)(blast) Do you know the game “Pit Pot?”
(G,4)(suicide) On the topmost row, hit the wall on the right side of the third room from the right eight times.
(H,5)(blast) On the lowest row, the wall on the right side of the second room from the left will collapse.
(E,2)(blast) On the second row from the top, the first room from the right is a hidden room.
(I,6)(blast) On the seventh row from the top, in the fourth room from the left, input the suicide command!
(I,8)(suicide) Think again!
(J,5)(blast) On the topmost row, hit the wall on the left side of the the first room from the left eight times.
(J,2)(suicide) Remember Alex Kidd in Miracle World, okay?
(M,7)(suicide) Won’t that make everyone sad?
(N,7)(blast) On the fourth row from the top, input the suicide command in the second room from the left!
Evade an attack while standing.
Push the jump button for just a short time; or, with the jump button held but before jumping, the head portion won’t take the hit, so you can immediately be able to block(?) the attack.
Judging from the hidden messages, they must be from the Pit Pit / Alex Kidd gang.