Conjure Mushmover

This is an incredibly versatile ability. It used to be a spell (and it uses the spell button to cast) but is considered an ability on account of it not costing MP. While it doesn't cost MP that doesn't mean you can use it infinitely. If you hit it 6 times with your sword it breaks and gives you 20 MP. This costs 1 mushmover charge (to the bottom right of your MP). Once you run out of charges, you can still place a mushmover but it won't give you MP from destroying it. It is great for spells but not so great for healing, since healing is a percentage. This ability can shatter progression. It has the most skip potential of any ability. 
See the Skips and Tech page for more info on all of these uses.
The first technique is called mushmoving. It was found by Jeshguin. You can abuse the backwards push of placing a mushmover to increase your speed. 
The second is the MG or mush gain. The most simple it involves placing your mushmover right as you jump. This will make your jump even higher. Alternatively you can pogo your mushmover which gives a bit more height.
The third is the MDP or mush destroy pogo. To explain it simply you destroy the mushmover to do a AMP (ariel mushmover pogo). You can use spikes or just hitting it 6 times to do this. 
The fourth and final is the SCP. This is by far the hardest. You need the summon mushmover ability and another spell. using the switch spells button you can eliminate the spell down time in between the recalling and placing. This can be used to gain infinite height.