How do I Implement Jumping into my ARPG with 8 directional movement?

Right now I'm thinking of using a side scroller beat em up as the template form my ARPG and building around it.

Growing up I loved games like Alundra and LoZ and I want to merge the 2 with my own take on a combat system. However I cant figure out the jump mechanics.

Please help, I'm open to all possibilities and have already tried tricked "tricks" with shadow animations

It's difficult to tell what purpose a jump mechanic would have in your game. In the kind of game you're describing it would be a jump animation for the character with the shadow included in the animation but in those kind of games, you don't jump. You could do something like move with 8-direction or the tile movement behaviour in a direction and play the animation.

Jumping in my game serves a purpose in combat and in puzzle solving. Jump over enemy projectiles for example. Jump onto a moving platform after hitting a switch. I realize that it is not possible to jump per say. And I've seen the jump animation technique by manipulating shadows under the player.

I guess my real question is how to accomplish the mechanical application of jumping in terms of evasion or reaching "higher" levels.

I had the idea of making a sidescroller beat em up (jump attacks are common in this genre) then adding in animations to the character to simulate the top-down adventure style.

Not sure where to go with this, but you may have guessed I have a lofty idea. In the past I have only made platformers so I'm really at a loss.

Any help is welcome

Well you're in luck as there is a new feature called Z elevation which might be useful in providing an illusion of jumping, it allows an object to change its Z so it looks like you're jumping towards the camera, or platforms are lower in the space :

Z elevation

The instance's elevation on the Z axis. By default the camera is at Z = 100, and looking down to Z = 0. The default Z elevation is 0. Increasing it will move it upwards (towards the camera) and decreasing it will move it downwards (away from the camera).

youtube.com/watch

If you don't want to use this, you would just mimic it with an animation and scaling the character.

In terms of dodging projectiles you would have a state where player is jumping on a jump key pressed, not like in platform behaviour, for this you would have to create your own variable isJumping and toggle it on and off. Then you would say when player isJumping, disable collision on the player. This would mean that enemy projectiles no longer touch the player. You could also do it the opposite way, projectiles do damage or explode if projectiles overlapping player and player is not jumping.

As you are unsure of the design yourself I guess that makes sense why the original post is confusing. To have a 2D side scrolling beat em up combined with a top down 2D RPG doesn't make too much sense. But the information above should help you to mimic jumping from a top down view.