Combining defensive tank abilities with a great deal of mobility, Overwatch's D.Va is a tricky yet versatile hero who can fulfill a number of roles when out in the field. When pushing against an objective, she can act as a frontline defense, but if enemy defensive heroes are causing trouble her Boosters allow her to get behind them and clean them out. She's also unique in that when she is killed her mech is destroyed but she escapes to continue the fight on foot. In this form, she's much weaker but still capable of harassing the opponent until a replacement is ready. She's best suited to players who like variety and juggling multiple responsibilities at once.
Fusion Cannons [LMB] - D.Va's Fusion Cannons are unique in that the closer you are to a target the more damage they do. This requires a bit of experimenting before you'll start to become comfortable with the damage falloff and how to dictate range against various heroees. She also moves slower while the cannons are firing.
Defense Matrix [E] - This is one of D.Va's strongest abilities because it allows her to negate all incoming projectile damage for a few seconds. Next time Soldier 76 pops his ultimate, instead of fleeing for cover your team can form up behind you and let you negate the threat. The medium-length cooldown will require some thought about when is the best time to use it, though. Ideally, you always want to use Defense Matrix to defend a teammate rather than just absorb some incoming damage.
Boosters [LShift] - What makes D.Va such a versatile threat is her ability to fly for a short period of time using her Boosters. They're on such a short cooldown that they can be used without hesitation, whether to escape a fight or get back into one much quicker after death. If enemy defensive heroes or supports are causing problems from the back, D.Va can use her boosters to keep them in check with her Fusion Cannons.
Self-Destruct/Call Mech [Q] - Self-destruct is one of the most fun ultimates to use in Overwatch because of all the ways in which it can absolutely ruin the other team's day. When the ability is ready, press Q to eject from the mech which will overheat and explode mere seconds later, killing any enemies within a large radius around the mech. This can be used with D.Va's Boosters to push the mech right into an enemy formation, just be aware that Self-Destruct can kill D.Va if she doesn't get far enough away. Afterwards, D.Va will be on her own and vulernable until she either dies or the ultimate recharges and she can call down a replacement mech.
Eject! [Passive] - Whenever D.Va takes enough damage, she'll bail out of her mech and go on foot. She'll only have her Light Gun during this time. It's a surprisingly effective gun across all ranges, but she also has the defenses of a wet paper napkin while on foot.
D.Va Strategy Tips
D.Va is a versatile tank that requires a strong understanding of when to flank enemy positions using her Boosters or when to lead the charge on the frontline. Her Fusion Cannons can be frustrating for those who have an aversion to getting right into the thick of combat, but that's where she's at her best.
Try to avoid using Defense Matrix except when it's absolutely necessary to escape incoming damage as smart enemies will be trying to bait you into using it early so they can follow up with a much more devastating attack after it's on cooldown. It can also be used to stop various projectile-based ultimates, making D.Va an incredibly effective tank during those final moments of a push when everyone is unleashing their strongest attacks to save the match.
Using the Boosters will also require a bit of finesse. While closing distances or flanking enemies are obvious uses, good D.Va players will use them to pull an enemy's attention away from the objective or make D.Va a tougher target to hit.
Finally, her Self-Destruct can be an incredibly satisfying ultimate when used properly. Firing your boosters to charge forward before triggering the ability can send a clumped up enemy team a package they weren't expecting, but there's more creative uses too. When squaring off against heroes like Roadhog, who can pull you in with his hook, a Self-Destruct can make them think twice about hooking you ever again.
Once D.Va is out of her mech, she loses almost all of her utility and will have to wait for her ultimate to charge before calling in a replacement. Unless you really need bodies on an objective, like during a final push to capture a point, you're probably better served playing aggressively and getting yourself killed so you can respawn in the mech and boost back into the battle rather than running around doing okay damage.