The Red Son Pack is a rotating pack (not always in store) that can be bought for 400,000 Power Credits and gives you any 3 Red Son characters:

Red Son pack

The Red Son Pack was one of the most classic ways to advance in the game, due to its low cost (at an average of 133,333 credits per character, they are cheaper than any gold card other than Black Adam/Regime and The Flash/Elseworld; Gold Booster Packs are also cheaper but is very unreliable and would very commonly yield weakest characters) and all-round strength in the ready-made team (it used to be a fixed pack with just Red Son Superman, Wonder Woman and Solomon Grundy), with +75% basic attack damage, +45% power generation and health for all three members, prior to the change to a random pack.

It was one of the cheapest possible ways to successfully complete Bonus Battle 6; they can beat it at ~EIII even prior to the introduction of gear, and they could be seen very commonly in medium levels of play in multiplayer, although their popularity inevitably slipped over time from the newer and more powerful Challenge Mode characters. However, with the release of augments (particularly crit augments), as well as more gear with difficult-to-avoid tag in stuns (LexCorp Gauntlets V2, Batman's Cowl, etc.), Red Son Green Lantern's crit/stun immunity has risen back into popularity. However, there is a decreased likelihood of obtaining the rarer Red Son varieties, specifically Red Son Solomon Grundy and Red Son Green Lantern.