Okay, for those of you who don't know, I'm a D.Va main myself.

Pixel Spray - "Shot Down": Prevent 1500 damage with a single use of D.Va's Defense matrix in Quick or Competitive play.

This one was probably the easiest achievement I've ever gotten.

This is how I got the achievement.

We were on attack on Temple of Anubis. We're trying to cap the second point but we can't even get close to it.

So a Roadhog comes out of the archway, and uses his Ultimate.

I basically ate his whole Ult while laughing like an idiot XD

A good strategy for this is to absorb someone's Ult.
Dva can absorb the following ults.
-Tracer's Pulse Bomb
-Pharah's Rocket Barrage
-Roadhog's Whole hog
-Soldier:76's Tactical visor
-Reaper's Death Blossom
-Mei's Blizzard(only her robot though)
-McCree's High Noon
-Zarya's Graviton Surge

I'd recommend absorbing Roadhog ults, And Pharah ults.

Cute Spray - "Game Over": Kill four enemies with a single use of D.Va's self destruct in Quick or Competetive play.

This achievement right here took me a month of playing quick play to get.

I got it on Hanamura Defense, first point.

A tip is to use D.Va's boosters to launch her mech into the air. Preferably over walls where the enemy team is.

This achievement will be easy as long as you can flank the enemy team, or even launch your Ult as is.

I hope this was helpful!