When you start the game, you only have the title character - Mr. Autofire. As you proceed in the game you will unlock more heroes.
How to unlock Heroes for free:
- The daily weekday events (Metal Monday, Toxic Tuesday, etc) will drop 1 shard more often than not, so in approx. 10 weeks you should be able to unlock the remaining Open A heroes (details on classification): Dr. Toxic, Frostina, Blazia and Hecate
- You get a free Summon gate every week, which will yield 2-10 Shards of an Open hero
- Once you are able to play the daily weekday events at Hard level, you have chances of getting Castle keys, and in the castles you can get Open B hero shards as drops and there’s also some shards as one-time clear rewards
- Shards can also be offered as Promo Codes, Login Bonuses or in events like Golden Pig or Gambit (usually it’s only coins but the July 2022 event had shards)
- The Tower Shop features shards for some Premium Heroes but it will take you a quite a while to earn enough points (you have to complete World 5 even to have access to the Tower Tournament)
How to pay to speed up unlocking Heroes:
- There are offers (I think only for Dr. Toxic) where you can directly pay and unlock the hero
- If you buy the Battle Pass or Super Battle Pass, you will usually get some shards as track rewards
- The Recruitment Poster from the SBP can be used to unlock Heroes (recommendation)
- You can use gems to open regular Summon Gates (you could do this even with gems farmed for free but you won’t be able to do it often enough to make a difference)
- You can use gems to open special Summons Gates (which either feature an Open Hero with Double Chance or a Restricted/Premium Hero without Double Chance)