Reaching a PSE Burst
PSEs (Photon Sensitive Effect) are boosts that appear in the top right of the Screen. The higher the level, the better the boost will become. PSEs will level up when enemies are defeated and a pillar of condensed photons shoot out of the enemy.
As a side note: A lot of information has spread about Reaching PSEs and what not, but it is really just defeating enemies and hoping for the best.
Reaching a Level 8 on a PSE will give you a chance at achieving a PSE Burst. Enemies will start spawning in the location of the Players. Once an enemy is defeated and the corresponding PSE appears again a PSE Burst will occur.
PSE Burst!
Once you've PSE Burst, all the players will want to stick together. Enemies will now rapidly spawn in your location. You'll still be able to generate PSEs while in a Burst. There is also a chance of receive a ONE MORE and extending your Burst.
Cross Bursts can be achieved by reaching more than one Level 8 PSE. Once a Cross Burst is reached, there will be a guaranteed ONE MORE.