I have two bugs I found in PM:TTYD as well.
At the Riverside Station, go into the room with all the cogs. Switch Flurrie as your current partner. Jump onto the cogs that can drop you when you first enter the room. Before you drop, use Flurrie's ability. When you fall, Flurrie will be stuck facing one direction no matter what. Also, if you repeat the procedure using Vivian's ability, the shadow will fall but then hang in mid-air. And if you are riding Yoshi, jump off him right before you fall off the cog. Yoshi will remain standing in mid-air until you hit the ground.
In Glitzville, go onto the Juice Bar and onto the Airplane platform. Transform into an airplane. As soon as Mario is no longer above the bar, press B to turn back into his original form. He will fall through the blanket thing covering the crates, and is able to walk around in them. Leave them, and it's normal again.
"My spirit burns like the sun and I shall dry you like a prune."