As with the M808C Scorpion, unless there is a large amount of infantry who can inflict large damage to you, let your gunner eliminate them. Vehicles, if present, are always your first priority.
You should always try to give your allies good weapons, like the Rocket Launcher or Incineration Cannon. Unlike the M808C, NPC allies can only ride on the front sides of the M820, as there are not enough NPC allies to sit at the rear.
The M820 is only available in the missions Glassed (in a Corp variant) and Genesis.
On higher difficulty levels, the Scorpion is highly vulnerable to being disabled by a Plasma Pistol overcharge shot, Splinter Grenade, or the Warden Eternal's head beams. Any sign of anything charging a charged Plasma Pistol shot or throwing a Splinter Grenade should be eliminated as soon as possible.
Like with the M808C, another popular tactic with the M820 is to use a "hull-down" position. The tactic essentially requires the tank to be positioned such that its hull (the main part of the vehicle) is behind a crest or other raised ground, but its turret (or a superstructure or roof-mounted weapon) is exposed.
Equipped with a powerful gun, the Scorpion can easily take out any aircraft it lays its eyes on. A way to counter this is to position your aircraft directly above the tank where its "blind spot" is. Then lower the aircraft on top of the tank keeping sure that you're still in its blind spot. Then, get out of the aircraft and jump on it and stick it with a grenade effectively destroying the tank. This tactic is primarily for use by the Wasp and Phaeton with them being the only two vehicles in Halo 5: Guardians with VTOL technology. This tactic can still be employed with the Banshee, but with a less effective outcome.
Using a Splinter Grenade, Plasma Pistol overcharge, the Grinder, or Echidna missile will temporarily disable the tank's mobility and greatly weaken its driver. As the tank's weaponry also becomes disabled, it is more vulnerable to being boarded or destroyed by other enemies, especially the Legendary or Mythic Warden Eternal or Goblins in Warzone Firefight.
An effective hijacking/boarding technique is to use active camouflage (either from a power-up or from the Prophets' Bane) and wait for the tank to pass by or approach the player.
Unlike previous games, Halo 5: Guardians features multiple variants of the M820 Scorpion:
Corp Scorpion: a rugged variant with slightly more armor, prominently featured in the campaign mission Glassed (as mentioned above).
Tundra Scorpion, Urban Scorpion, and Woodland Scorpion: improved variants with more armor than the Corp model.
ONI Scorpion: an advanced Scorpion with even heavier armor than the Urban model and upgraded experimental ammunition, useful for dishing out even more damage on large enemies on the ground.
Hannibal Scorpion: an advanced Scorpion with directed energy weaponry based on those of the Spartan Laser and Hannibal Mantis, making it very useful for dealing with aerial targets and Legendary or Mythic Warzone bosses. The hitscan nature of its weapons also helps greatly against fast-moving targets.