What are some games which when you get good enough at it allow you to blast through it at the speed of light compared to when you first started out at it, where displays of skill are tantamount to a speedrun?
One such game would be Alien Soldier, which has a mechanic where if you are at full health, your dash becomes a phoenix of fire which tears through everything in its path and can even oneshot some bosses. But doing so also sacrifices a bit of health so you can't keep spamming it, so you need to parry a projectile in order to turn it into health so you can keep Phoenix Forcing again and again. Though this gets harder if you take too much damage. There is a satisfying feedback loop going on of don't get hit->kill things faster->get less likely to hit because you are killing everything so fast->kill everything even faster, so speedruns of Alein Soldier are very impressive to look at.
There's also a similar POW-item mechanic in games like Shinobi, Castlevania Bloodlines, and to some extent Mario where you can find an item which lets you deal increased damage, but it disappears when you get hit, the idea again being that getting hit less lets you kill faster.
Are there more games which work like this?