Mario Secret Message Game

Mario Secret Message Game, also referred to as Get the message? by its card and description, was a post in the News section released on Play Nintendo's website. The challenge of the post was to solve a cryptogram.

Questions
The solution is marked with a green border.

Letters
Each letter is represented by an item, block, or enemy.
 * A - Buzzy Beetle
 * B - Koopa Troopa (unused)
 * C - Hammer Bro (unused)
 * D - Piranha Plant
 * E - Red Shell (unused)
 * F - Green Shell (unused)
 * G - Warp Pipe (unused)
 * H - Note Block
 * I - Empty Block
 * J - POW Block (unused)
 * K - Brick Block (unused)
 * L - Goomba (unused)
 * M - ? Block
 * N - Yoshi's Egg (unused)
 * O - Propeller Mushroom
 * P - 1-Up Mushroom
 * Q - Super Star (unused)
 * R - Fire Flower
 * S - Super Mushroom (unused)
 * T - Coin (unused)
 * U - Bob-omb (unused)
 * V - Lakitu (unused)
 * W - Monty Mole (unused)
 * X - Boo (unused)
 * Y - Thwomp
 * Z - Cheep Cheep (unused)

Description
''In honor of National Mario Day, we’ve written a super-duper secret message in a Mushroom Kingdom-inspired picture alphabet. Can you decode the message using the key below?''