Epic Seven if you never played before. Collab with guilty gear bring us very OP free 5* hero and It's not hard to get him even for a new players.
Short start guide for a new players
For servers, choose Global, after 10-10 (30 mins of gameplay or so) you get free 30 gacha reroll aka "Selective Summon". In this summon you must get Angelica (Healer and most important hero atm) + some DPS hero, Sez, Vildred, Cidd, Karin, Ken, Iseria or Aramintha. If you can't get them in first try, then reroll. Be sure to get Angelica since she very important.
Now just follow story mode and level up to 9, after that enter [Visitors from Another World] event and farm until you get Sol Badguy, his artifact, MolaGora Seed, 5 Covenant Bookmarks x3.
Sol Badguy a bit OP atm especially for a new players. 1 copy of him is enough, but if you can get all of them and SSS him it would be better and you can save on upgrade materials.
After you done it you can continue story mode to get free skystones, save them until good banner up.
Current banner - Baiken and she just average (can be buffed later) so no worth to roll for her, Dizzy banner will be up right after Baiken banner end.
First Epic Seven Collab - Guilty Gear. Old fighting game that still popular in asia.