His shards can be obtained by ranking in certain Arena seasons. He can also be received in the United Heroes chest and its shard version. Also in the JL chest and JL power up chest.
He seems to be one of the few (if not only) heroes to have a passive that cannot be upgraded.
Justice League The Flash is one of the deadliest opponents due to his high speed and damage; as a high threat opponent, he can often instantly KO your heroes in a single jump or ranged hit (with Justice League Cyborg massively buffing his already dangerous basic attacks). This has led to him, Justice League Aquaman and Justice League Cyborg being one of the most common Arena enemy team you will face, particularly in the 800k - 1.2m Threat range.
A viable strategy is to use a high-level Special block ability to greatly reduce damage and reflect it back to him, sometimes instantly bringing him to 1 health in extreme cases.
However, fighting him at full strength is still very difficult since you practically must block every single hit he does or be one-shot KO'ed, and he is so fast he is hard to counter. It may be a good idea to just tag (to gain power yourself) and retreat quickly while using ranged attacks to slow his advance, until he gets 3 bars, at which point he would usually use Speed Run which will let him hit you from any distance (which can be special blocked, and even while unblocked Speed Run usually doesn't do nearly as much damage as his basics.
Sonic Shock empowered by his passive sometimes breaks Special block on the last hit (while normally Special block ignores unblockable attacks). It also has a chance to stun, which is very likely if it is high level, making it very dangerous.
- The second half of Sonic Shock resembles the meter burn version of Speed Dodge on console.