Like most Magic: The Gathering cards, the value of Azorius Justiciar depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (Ravnica: Clue Edition)
The cheaper creatures in the deck are threats themselves, so The Gitrog Monster naturally survives in a lot of games
The more you can make sorting cards routine, the faster it will go
Aside from battling, you can also trade cards (it is a trading card game, after all) with users through an online trades marketplace, where you can put cards up for offer and browse cards other users are offering
Reyhan allows your creatures to lend each other their +1/+1 counters when they die, which can help to prevent lost time and mana investments