Sweety Mania
Merge Poppy Master lets you merge heroes to win battles. i found the controls are lazy but the action is intense, and the main mechanic is combining units to boost abilities.
Combine heroes with complementary skills to boost abilities, and plan your merges carefully.
No extra buttons or toggles are stated.
Focus on merging heroes that boost each other's abilities. Avoid merging randomly and watch what comes next to plan ahead.
Start combining units to win battles, then merge heroes with lazy controls but intense action, and I find the main mechanic is combining units to boost abilities, Merge Master: Merge Poppy is a Related game that requires careful planning for victory.