Echoes of a quartet, multiplied force, a leap from pair to foursome, fourfold strength in a single course.

Slayer of regrets, old and new, sought by many, found by few. What am I?

If you have me, I‘m inside your head, If I‘m a bad one, I might cause you to be dead, OP had to have me to be able to post this riddle, I have an even number of letters, so there‘s no single letter in the middle. What am I?

I’m born in the depths where no light ever gleams, Then rise to escape in a sigh or a scream. Some blame me, some claim me, some flee my offence I slip past your guard with a puff of suspense

I sparkle bright in gold or blue, a precious gem, but not brand new. Found in rings and royal flair, What stone am I, with regal air?