My HF note file has too many things to post here, and most of them are silly. E.g.:

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...But here are the actually (potentially) useful things I've found in the last few months!
An enemy slammed by an enemy who was frozen by an Iceberg Shower produces a Diamond.
It seems easier to react quickly to motion that you see out of the corner of your eye. I can almost never manage the teleporter hop on 95, except when I watch the top of the screen. Then I can react quickly enough to change sides. Weird...
On 95, if you have

, you can get to the effect item easily no matter which teleporter you emerge from. It's possible to jump up into Bombino 7's box from the right.

(I've also had this work without the shoes when the game was lagging enough.) Same effect, but less useful: you can jump up into the lemons' area on 44 from the little upraised spot on the left.
Pear bombs can still kill you when you're shielded, by bouncing you off a platform.

You can walk off and back onto a ledge without dropping a bomb. Just barely, though.
Grab the dragonfly BEFORE you complete CRISTAL.

Hitting a hopping bombino with two bombs in quick succession will prevent it from falling down through its ledge (at least sometimes).
If a letter and a pearl appear on the same spot, the game will register the pearl first, and you won't get the letter.
However, you can grab the last letter of CRISTAL and a magic card at the same time, if they're in the same spot, and get the benefits of both.
It's possible to take two letters at once, simultaneously forming one CRISTAL and getting a one-letter head start on the next.
Spikes don't kill unpeeled lychees.
Tuber can't hurt you when he's flashing.
On 86, you can turn the lemons into ricocheting ice cube traps to kill the leapers. Just bomb one of 'em when a leaper is heading toward it, but not close enough to be frozen along with it. Fun!
Even though a lemon
looks wider than a lemon drop, you can get closer to the lemon than you can to its projectile. Thus, when you can't dodge to the side of a lemon that's taking aim (e.g. when you're trapped under the lemon on 65), it's possible to dodge the drop by jumping straight up through the lemon's side.
It's impossible to diagonal-kick when you're directly facing a 1x1 barrier. Taller walls are okay for some reason.
You can easily get back into the starting box on 11.0 if you keep your red bomb. Good for collecting letters and crystal shards.
On the PD33 level with the bombino and apple, it might be best to leave the apple alive while you attempt to take the item if it's one you REALLY want. That way, missing the jump will only cost you a life and you can try for it again (rather than advancing to the next level without it).
Even if you don't eat the enemies on 33, Ghost Candy can still ruin the order if you eat the spikes. XD (Theoretically, it could ruin your whole game if you die after eating the spikes. That would leave no way to kill an apple once it gets up there.)
If you're being chased by a really angry apricot or banana, you can force it to pause by jumping up to the level above it. Even when they're charging around at top speed, they'll take just as long to pause and think before they go up. That can give you the extra moment you need for a planted bomb to freeze it.
You can't hit a raspberry that's on your platform with a bomb that you kick normally -- but you CAN freeze it with a diagonal kick. That bit of extra distance makes a difference!
Ninja spikes don't glow red if they appear after you've taken Ghost Candy -- but you can still eat them.

On 54.12.1.9G.3.7, always check to make sure the orange is really dead before you try to exit the level. Always always always.
You can avoid a lot of hassle on 15.10 by never taking the red bombs. Just clear out one side with the white bombs (preferably the left, since it has two apples), then just keep throwing bombs at the base of the pillar. The enemies will eventually come down within range, and away they'll go without you ever having to visit their side. You can sometimes clear out a few enemies on each side by repeatedly stepping off the top of the pillar, throwing a bomb and hopping back up while you wait for the items.
There's some margin for error in the game's deciding which enemy died first. If two fall down NEARLY simultaneously, with the earlier one in the order slightly behind the later, then it will still count as though the earlier one fell first. You can see that it didn't, though, by the fact that the green crystal comes down first.
When entering/exiting a PD in 2-Player mode, make sure that there are no spikes between the portal and the guy who's
not jumping in. If he crosses a spike when he's pulled into the portal, he'll die instantly on the other side.
...I have a lot more frivolous "discoveries," but this is already a wall-o'-text, so I'll save them for later.
