After releasing on Google Play and uploading the demo to Itch, I posted at Reddit and get a lot of feedback. 

Here is the changes in these three days.

• Remove the cost to reset hero skill tree, yay.
• The XP and copies required to rank up a hero have been reduced. 
• Add currencies drop tooltip. 
• The hit range of Lyra is reduced, but all the mobs can be summoned at the enemies' positions.
• To celebrate Christmas, Danta is now available in the demo.
• Balancing tweak to make it easier to pass through first waves for most heroes 
• Skill tree reset button size tweak, and a "Insufficient Ruby" hint added
• Currencies panel is always visible
• Display a different outline for more important nodes in the research tree
• You can get some hints from heroes wandering in the castle
• Reduced the default BGM and SFX volume
• All four elemental statues added
• Hero's speech bubble can be toggled on/off
• Fix split projectiles position issue
• Hero XP Pack can affect the rank XP of future gained heroes
• All uncommon heroes are available in the demo
• Building upgrade costs have been reduced
• Reduced the cost of game speed research and increased max game speed to 2.5
• Reduced the cost of the Unlock Auto Choose research cost to improve QoL