I created two enemy characters who can be suitable for SMBX. One who replaces the Tweeter and another who replaces the Ripper.
Starting with Mips, the yellow rabbit.
As a demonstration, Mips can jump like a Tweeter. Mario can stop him and Mips appear in friendly mode after being caught. He can give him a star.
And for the end: Klepto
I tried to place a 1-up mushroom in order to make Klepto look like that it's stealing it. But, the mushroom didn't connect to him after I tested it.
Credit to Mariofan230 and Izzi Rae
Download
Download 2