ACA NEOGEO METAL SLUG X

This is a complete achievement walk-through with a successful 1.5mill run of HI SCORE MODE video with constant commentary explaining everything to look for when attempting these achievements. I can guarantee you will limit the amount of play-throughs needed by watching/reading this

ORIGINAL Mode: Use the walkthrough to see how to maximize points in the first 2 missions, then combine that with the save trick mentioned below to achieve 2,000,000 points.
CARAVAN Mode: "Get as many points as you can in 5 Mins" So basically follow the walkthrough for Mission 1 and these cheevs shouldn't be a problem.
*Can be glitchy I got 900k and only unlocked the 500k achievement...it wasn't until I "Quit" the game and reloaded it that it worked, but only after I reached the required score again.*
HI SCORE MODE: To get 1.5mill w/o continues...this is the main focus of this video follow the tips and watch the playthrough for your best chance at success. Practice makes perfect here!

*ALL TIPS / Text Guide*
GENERAL TIPS
1 - Melee kills are worth 500 points opposed to 100 for shooting them
2 - Grab ALL treasure, some can be random from 100-30000 points at some spots
3 - Ride vehicles to the end for big points
4 - Each POW saved = 10000 points & 30000 points for the backpack girl **you must walk into her!**
5 - Practice makes perfect, other than random rewards everything else stays the same combat-wise

ORIGINAL MODE ONLY Tips
- You can use the “Creat Interrupt Save Data” option to create a Save exactly where you paused your game,
and if you die you can just hit the button on your controller and “Quit” Metal Slug X.
- When you reload ORIGINAL mode it will put you back exactly where you saved. BE CAREFUL not to save right
before you are about to die trapping yourself in an endless death loop.
- Use this walk-through to see how to maximize your points in the first 2 missions, leaving you with decent
wiggle room for the 2 mill.

MISSION 1 Tips
1 - Grab the Camel! It's worth 400,000 points compared to the 200,000 for the tank.
2 - Right before you get on the Camel throw grenades to kill the Arabian on the other camel to avoid a tough camel battle.
3 - Just after the camel sequence there is a reward that shows up on the top level which most of the time is a 30,000 point gem, but sometime it's a sh**ty apple worth 100...restart if this happens.
4 - At the HELICOPTER section make sure to KILL THE RED ONE 1ST as it will give you an extra 125,000 points!! :o
5 - The last 3 POW's are underneath the BOSS after you destroy the under turret. Make sure to grab them before one walks off the screen! P.s. It is safe to go under there with your camel.

MISSION 2 Tips
1 - I would avoid using melee on the mummy enemies. Once mummified you can change safely back if you find a glowy potion somewhere before you are hit with the purple haze again.
2 - The "Bee Mummies" were my worst enemy, I suggest you get the green mummies as soon as you can to avoid any frustration.
3 - Just after the first 2 "Bee Mummies" there is a corpse in the lower-right corner. Interact with it for 50,000 points, but quickly run away as the corpse blows up right after!
4 - There are 3 RNG reward sections that can contain 30,000 points in this mission, I point them out in the video.
5 - "BTW, when you get to that metal tower with the 4m sign on it around 7:40, there's a POW hidden above it, just keep shooting up and he'll eventually drop." - Thanks @EarthboundX
6 - End the level in the Mech vehicle to get 200,000 points. If you are hit twice while in the Mech, then you will have no turrets forcing you to get out if you want to finish the level.

MISSION 3 "Clean-Up"
1 - Mop up the rest of your points here if you didn't get it at the end of Mission 2.
2 - Take it slow, grabbing all the goodies and melee killing enemies when you have the chance!
3 - Most people should have 1.5m by the time they get to the boat section that starts with 2 POW's on the train w/ one giving you a weapon upgrade. If you don't have it by here you probably won't make it.

TIMESTAMPS:
00:01 - Tips Explained
01:43 - Mission 1 Ended w/ 911,000 Points
06:02 - Mission 2 Ended w/ 1,474,000 Points
12:52 - Mission 3 Clean Up
15:47 - ORIGINAL Mode "Save Trick"

To make this as stress free as possible you'll want to finish the first two levels with preferably all the POW's, not die at all, and finish in the vehicles.
In the first level try to;

gather all the extra gems and coins
-Ensure you find all 13 POW's
-When you reach the group of helicopters make sure you destroy the red one first and the others will follow, gifting huge points
-Finish the boss in the tank, but after destroying the turret on the bottom which reveals three more POW's

In the second level try to cover the same as above really, some moments to consider;

-There's a POW hidden in the first tunnel the mummy walks out from
-the corpse on the right most of the screen before you travel up has some goodies but remember to jump out the way after shooting it!
-Finish in the vehicle
-also if you turn into a mummy don't give up, its fairly easy to keep on until finding a potion

Granted you made it to the third level this way you should potentially have 1.2 - 1.4 million already, so practice the run of the third level and you should hit the 1.5! I believe I got it shortly after taking down the boats, and just after the red jet plane arrives (where you jump to the train)

MightyAxe's solution is on point, but if you'd like to see a successful achievement-unlocking playthrough in video form, check this out below:

I just found the videos of level one and two with all the bonuses. if all goes well we exceed 1.5m points at the end of level two.

Level one :

Level two :

Enjoy