Four and five-star Heroes are rare and powerful by design, but there are several ways to get them:

• Level 13 Training Camp unlocks Elite Training, with a chance for Epic Heroes
• Level 20 Training Camp unlocks Legendary Training, with a chance for both Legendary and Epic Heroes
• Wanted Mission rewards, high-level Titan loot, Mystic Tower, Challenge Events and Quests all have a chance of giving out Epic Summon Tokens
• Every Epic and Elemental Summon has a chance for a four or five-star Hero