https://youtu.be/3yagnJ4eJ-Q?si=vtS8f5dvQthaGdwv
Powerful tank with a main gun that inflicts 12 HP damage on a 9-tile radius, and Vulcan cannons that hit twice when fired. Moderate fuel capacity means you need to be choosy about initial placement if it isn't already on the map to conserve fuel for firing the weapons as "ammo."
If your Metal Slug blows up while your character is inside, the character is "dead" for the mission duration and can NOT be revived during the mission.

Best way to avoid that situation - if you can obtain it - is to get the Alice Activation special action, which can remotely control a vehicle for two turns (as many times as you want to keep using the action during a mission) via holographic driver.
You can only EXIT Metal Slug (or Slugnoid) at the START of a turn, before you've performed any movement or attack actions with the vehicle.

• Armor (hit points): 25
  
• Fuel: 150
  
• Movement Fuel Cost: 4 fuel per tile moved
  
• Main Gun Fuel Cost: 25 fuel per shot
  
• Vulcan Cannon Fuel Cost: 10 fuel per shot

• Main Gun Damage: 12 HP per tile
  
• Area of Effect: 9-tile targeting area

• Vulcan Cannon: 8 HP (2 hits at 4 HP per hit)
  
• Targeting Area: Single tile
  
• Friendly Fire Note: If a friendly unit is BEHIND an enemy that your Slugnoid is firing at, the friendly unit will take some light friendly fire from the Vulcan Cannon.
  
  
• ENEMIES NOTES: Vulcan Cannon does +1 dmg (9 HP instead of 8 HP) against the Convoy Truck. It's worth noting if you decide to use either vehicle during the Convoy Truck mission.

https://youtu.be/nb9j1eSWPQ4?si=dCNbcvx2lsbSjLm1
Desert Zone Boss
Metal Slug is super effective against the Big Shiee battle ship boss, but just be sure to drop it on the platform to the right/east of your character's starting point, since the tank can't cross gaps in terrain.

Also, due to how cramped the first harbor platform is, you can find it difficult to maneuver. Make sure your soldiers can still have clear firing and/or melee lanes to the boss ship, and that they aren't situated in front of the tank - otherwise it can't use its weapons safely. :)

Tombs Boss (aka Cobra Robot)
CAUTION: Neither Metal Slug *nor* Slugnoid can survive the ground transformation that occurs on this boss fight immediately after the cobra boss unleashes its death ray beam that annihilates everything except what's on a few "safe tiles" beyond metal plate shields.

HOWEVER, for whatever reason (development bug or by design), the ensuing ground transformation/shifting that then occurs instantly DESTROYS either vehicle and the character inside them.

So my advice is when the animated tiles show you that the death ray beam attack is next, EXIT the Metal Slug or Slugnoid and move the character to one of the safe tiles behind armored plates. IF the character initially still shows up as a corpse in the next turn after the death ray beam/ground transformation, just wait a turn and then you should finally be able to use a 1Up token on that character. But if the character was inside a vehicle, it can't be revived during the remainder of the boss fight.

If when you exit the Metal Slug/Slugnoid, the character can't reach a safe tile, then Undo your move, and go ahead and use the vehicle one last time to do some final damage to the boss.

Jungle Zone Boss
Metal Slug's movement on the Jungle Zone boss is badly hindered by the gaps between the platforms, which the tank can't move across; and by the changes in elevation, given that the tank's main gun and cannons can NOT reach targets located on different elevations.

So you're better off with the Slugnoid suit on this boss level, if you have the luxury of that Asset choice. :)

Scirocco Boss
On the final boss, Metal Slug's helpful in depleting boss HP and destroying incubator capsules; however, given its limited fuel (which serves too as ammo), try to not move the Slug more than is necessary to avoid being destroyed by the "marked for destruction" pink, rectangular field of tile animations.

Also, a single Metal Slug Vulcan cannon shot can rip through TWO capsules if you line them up in a row.

https://youtu.be/MCXyT_RvlNI?si=486iicKklR7yX28w
I describe Slugnoid as a mix of the Aliens movie's power loader and Iron Man's jet boots, combined with a couple rotary cannons. :)
Unlike with Metal Slug, if your Slugnoid blows up while your character is inside, the character's corpse will appear on the ground and CAN be revived via 1UP token.

You can only EXIT Slugnoid (or Metal Slug) at the START of a turn, before you've performed any movement or attack actions with the vehicle.

Vital Stats
• Fuel: 200
  
• Armor (hit points): 20

• Movement: 4 fuel per tile movement
  
• Vulcan Cannon Firing: 10 fuel per shot

https://youtu.be/vNAkoYSxHXE?si=eQ7fMyq5bZPXdDqh

• Vulcan Cannon Armor (HP): 8 HP (2 hits at 4 HP per hit)
  
• Targeting Area: Single tile
  
• ENEMIES NOTES: Vulcan Cannon does +1 dmg (9 HP instead of 8 HP) against the Convoy Truck. It's worth noting if you decide to use either vehicle during the Convoy Truck mission.

Most often you'll obtain this via an Asset Reward after completing a mission.

On occasion you be able to purchase it as a Resupply asset item in the Shop screen at the Hub you visit after completing a region's missions and boss encounter.

Far less frequently, some missions, including the Escort Rumi mission in the above video, will have Slugnoid already placed on the map.
All-Terrain: Slugnoid's hovering ability enables it to traverse any floor gaps and height elevation changes in the environment, so you don't have to worry about the environment inhibiting its movement as is sometimes the case with the Metal Slug tank.

Fuel Efficient: Slugnoid gets 200 fuel to start. From my calculations, it consumes roughly 4.67 fuel per tile movement.

Its two cannons each consume only 10 fuel per shot.