Mario Secret Message Fun Decoding

Mario Secret Message Fun Decoding, also referred to as Homework cat-astrophe! by its card and description, is a post about Super Mario Maker 2 in the News section released on Play Nintendo's website. The challenge of the post is 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
 * D - Piranha Plant (unused)
 * E - Red Shell (unused)
 * F - Green Shell
 * G - Warp Pipe (unused)
 * H - Note Block
 * I - Empty Block (unused)
 * 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
 * T - Coin
 * U - Bob-omb (unused)
 * V - Lakitu (unused)
 * W - Monty Mole (unused)
 * X - Boo (unused)
 * Y - Thwomp (unused)
 * Z - Cheep Cheep (unused)

Description
''Cat Mario worked hard on his first homework of the school year, but his friend Undodog accidentally made it disappear—woof! Can you decode the message below to find out what Cat Mario will do? Undodog and Cat Mario appear in the Super Mario Maker 2 game, available now for the Nintendo Switch system.''