The Mysterious Gravity
The only thing mysterious about gravity it is gravity itself. While you can define gravity in different ways for instance attraction of two massive objects , where one could have a greater mass then the other object , or both could have equal mass. Another explanation could be that gravity slow down the moving object for instance slowing the rate of expanding universe.
What is gravity made up of ?
Considering that every matter or anti matter is made up of somewhat elementary particles and their antis, We know that Gluon are the strong force , W and Z bosons are the weak forces and electromagnetism which is carried by photons. Gravity which is as the fourth force, Considering it particle-less then how do we really know that gravity exist ?
Is Gravity a Wave ?
General relativity, tells us that curvature movement in space-time is what we known as gravity , Let me explain you guys more briefly, We know the famous example of bowling ball on trampoline fabric , As you put the ball the fabric cause a depth , which bend down it's fabric towards the bowling ball. Further more, where ever that ball moves the fabric moves with it. Now imagine this bowling ball as our Sun , when the Sun spins it creates gravitational waves. how come waves are able to attract two bodies ? This is another mystery yet to solve.
Tachyons are hypothetical particles that travels at the speed of light , Photons on the other hand are light particles proven to exist , Gravitons on the other hand are virtual particles of gravity. Scientist have not discovered these particles as they consider to have tiny mass. If this particle will discover it will confirm the definition of gravity and bring out some more flaw in General relativity.
In the nutshell
The mysterious gravity still needs to be completed , Sir Newton could not be able to described it fully , while Einstein reaches some of its way to show what gravity could. However gravity remain a mystery , Whilst studying my whole life that gravity attracts two objects , I still not believe that gravity is an fundamental force , I would say that gravity is just an illusion .