More stuff that might or might not be known!
On
this level in PD15, you can get an undocumented gold coin by falling off the platform on the right (with the orange) and landing two levels below it (where the apricot is shown).
There's another undocumented coin on the
last level of PD51. Bomb-hop onto the lone square over the Jewel, and it will appear in the narrow pit beside the altar.
There's an easy way to get the order on
43 if you have running shoes (and, I think, two bombs): arrive on the right, and wait just above Fruit #3. When it reaches the end of its platform, since you're still above it, it will (hopefully) turn and start walking right. As soon as it turns, drop down, bomb-hop across to the #1 lemon and knock it down before Mr. Apple comes back. From there it's a piece of cake.
And I don't even know HOW this happened, but... apparently you can make bombinos explode with a blue bomb?

I was
here in PD64 the other day, with both bombinos on the lower right platform (nearest to bombino #1 in the picture). I tossed a blue bomb up there and they both fell down, flashed, and blew up next to a very surprised Igor.
Maybe it's something to do with the fact that the level is icy? I noticed the other enemies would behave oddly when defeated, sometimes flying off at strange angles (nearly horizontally, and faster than usual). I wonder if it's a glitch.