Wall jump - you can wall jump in this game on full magazine. Try it out.

Combos - if you do not land on floor between killing enemies, that's combo. Bouncing and reloading off decorations does not break the combo.

8 kills - 100 gems
15 kills - 100 gems and +1 energy
25 kills - 100 gems and +1 energy and +1 health

Increase max HP - getting health 4 times when at full health increases max HP by 1. This also works with Apple.

Shop keeper prices - they do not rise proportionally. For example, from world 1 to last world, battery raises it's price by 500%, curry by 80%.

Hard mode is granted upon completion. It's nicely done, different enemies and different level mechanics instead of tweaking HP.

Boulder style - while +2 HP seems like a good idea, reducing upgrade selection make your run luck dependent. It also makes you fall a bit faster, which game doesn't tell you.

Floating style - it's ok. I used this for practicing combos.

Head stand style - 30% discount and no upgrades - worst style.

Arms style - This one is the best. All caves will have +1 health or +2 energy. Rare shops is not important flaw, and reverted with one upgrade anyway.

Top tier:

Youth - helps pick up top tier and avoid meh tier.
Safety Jetpack - game changer.
Laser sight - now you're playing with power.
Gem attractor and
+ Gem powered - (almost) never runs out of gas.
+ Popping gems - fliers defense that shoots upwards.
Hot casing - fliers defense that shoots to the sides.
Candle - good idea to get before boss.
Drone - power varies on your weapon.

Okay tier:

Member's card - lets you find curry easier. Negates Arm style flaw.
Knife and fork - increase HP quickly if you play methodically. Unfortunately, on hard there is less opportunity to consume in peace. If you want to make this your strategy instead of combos, keep in mind that style can make it harder or easier to catch up to the bodies, they disappear fast.
Apple - can save a bad run, or turn into free curry.
Gem sick - rarely useful.
Reverse engineering - it also rerolls the health/energy bonus.
Rest in pieces - negates eating bodies, otherwise decent.
Timeout - candle is better.

Harmful tier:
I beat the game on hard without those. Maybe you will find uses, but for me, they are too messy. Changing how I wired my brain to jump on enemies and block, and mess around with falling speed mid game is not something I want.

Gunpowder blocks
Rocket jump
Blast module
Heart Balloon