ok, this game is one that "everyone see before", is more luck based than challeging - the swaps of the pieces are TOO slow, making the time critical, always critical.
So, make the pieces faster, and add a bit more time (or require less swaps to continue). At least, this is my first opinion for this game.
There is a bug with "The Great Hydra" storyline quest... the stage don't have ANY possible position to place units... just the road, sea and green pasture... no pavement...
The best way to grind levels, is buy magic and armor first, and do long combos...
The purple pigs at level 0 sword takes a combo for more 120 hits... lots of xp!
 "Fairy Nook"){kind=icon}
 "Protector IV"){kind=icon}
 "TinyRPG"){kind=icon}
 "Chibi Knight"){kind=icon}