Fun game. I had a lot of fun with it. The entire game as a whole is a bit grindy though.
I have a few issues, and suggestions if you plan on making an update to this game.
Unlocking heroes costs an insane amount considering their upgrade costs start lower than the purchase price by far... There's no reason for the cost to be that high to unlock them when the upgrade costs alone make you have to regrind through the same levels about 50 times just to get them to be useful by the time you can afford to unlock even one of them to begin with unless you plan to keep them at level 1. Also upgrading the troops is no where as rewarding as upgrading your heroes yet the cost is still high enough to compete since the diamonds take progressively longer to grind up in the later levels (Time to diamond gain ratio unless you are magically over upgraded). Also upgrading the castle feels almost pointless. You get an extra 2-4 Angel Bunnies but you spend so much time not sending out new troops to save up to upgrade it that your waves get pushed back, and then you can't summon enough of them no matter how much money you have saved up while trying to save up to upgrade your castle. If the castle upgrade gave a buff of some sort, or even just more defense to the castle it would make more sense to do. Similar issue with troops. Too costly. Wouldn't be so bad if the heroes leveled up through experience/usage instead. It would help you save up diamonds to upgrade the troops. Could keep diamond cost to unlock the hero which would make more sense considering the upgrade prices are so low at level 1 yet costs insanely high to unlock. Wouldn't mess with any medals either since there's no medal for leveling up the heroes. Just unlocking them all.
Also not sure if you are aware of this but Pipsqueak's level 4 stats are better than the more costly Featherweight's stats at his level 4. (Might have been lower at earlier levels but I didn't notice this until at least level 4) Kind of off balanced there with the stats/cost of those two units.
Having life bars next to the hero boxes on the top left would be very helpful. Sometimes it's hard to tell which one is being hit during the boss stages since the small red bar over the sprites overlaps when they are all standing on top of each other, and their buff's overlap the hp bar as well but there's no animations to signify which one is being struck so you never know until one of them dies.
Also Rarity's power is pretty much useless. The buff runs out too quickly, and even with a few upgrades she only got 1 diamond off an enemy when she did get a kill if she was even the one to last hit the enemy in the first place. If it got a buff, and farmed more diamonds it would be worth having her. But otherwise she's a waste to ever use, or upgrade. With that said Pinkie's might be a bit over powered. 2x attack means she turns a team of 3 into a team of 6. Might want to tone her attack speed buff to 1.5x, or apply a higher attack speed but only to her like a Rogue, or Thief class since she did seem to have weaker attack.
Another suggestion is to add a flash quality button for people with slow computers. I was able to find a quality toggle but I had to right click, and enable the alternate flash menu, and then click quality. Not everyone knows how to change quality on flash games that way so for their sake it would be great to have one somewhere they could click on. This would especially help the somewhat laggy bonus game if people are getting lag there.
Thanks for making this game btw. The sprites were adorable, and the attacks were very neat.