One useful advice: mute the game automatically, when the player clicks on the advertisement for the temporary buff, otherwise they won't hear anything from the video. ;)
There must be a huge amount of fake/multi characters because I rarely get friend invitations, but when I do get some, it's always half a dozen at the same time and from characters of the exact same level. That also explains the rating which is still above 3 stars, despite the fact that actual people write only negative comments about the game here.
My strategy went as follows... At the Nebula shop buy the mega bomb (hotkey v). Don't spend gold on anything, instead go for best ship first. Category doesn't really matter, I chose the first and most balanced type. I replayed a few levels, but not much, around half a dozen times. Then buy the 6 best elite upgrades for your ship. Around level 15 you should have already completed 15 achievements, and the black market is open. If not, look up an explanation of the achievements, and try to complete a few more. Discard the elite upgrades, and buy 10 black market upgrades (including the one which gives you 4 additional slots). You can defeat Genu at this point, but it's a little tricky and requires some time and maneuvering. Alternatively, you can go for the legendary shop (the other one which appears in-game). I used the two cheapest upgrades from there: ultra bomb (hotkey v) and energy refill (hotkey f). Alternating between these two killed even Epic in about half a minute on level 25.
I just beat the game in 41 days on my first try (normal mode). And I never repeated a battle, except accidentally the first one once. The three boss battles were clearly the hardest, I lost a few times there, but others were ridiculously easy. And I didn't even use any special strategy or high level spells. I just spent all of my available skill points on attack, defense, speed and agility, and clicked like crazy, so most levels were done in one minute or so. Except for the boss battles, where I needed to try out a few spells too (meteorite seems to be the most effective against them).
I don't know the rest of the game, but the badge can be relatively easily collected. I used Viegraff, Popo, Grulborg, bought some new tier 4 or 5 units for them (I didn't even care whether melee or magic or whatever type they were), and used only those items I got after completing missions. I didn't evolve anything, didn't buy any new skills for the heroes, didn't use alchemy, titans, and any other shit which can be unlocked by money. And I didn't grind at all! There were some 3-4 missions which I needed to replay once or twice in order to pass, but that's all.
I don't have the slightest idea what happened, I was not even sure which wrestler I was controlling, but apparently I got both medium badges on my first try in like half a minute...
Still don't really know if it's a bug or deliberate feature that you can go up your fort and stay there or even sleep and regenerate during whole waves...
I started with the hard campaign, and completed it. Now I've got the hard badge but nothing more. What am I doing wrong? Why didn't I get the easy and the medium badge (the single player one)?
Almost completed the game on my first run using only the basic, level 1 sword. Well, and one raven of course, which did most of the killing, while I was running in circles or hiding in the corner. :D
 "That Pokeyman Thing Your Grandkids Are Into"){kind=icon}
 "Fleeing the Complex"){kind=icon}
 "Crusaders of the Lost Idols"){kind=icon}
 "Forge of Gods"){kind=icon}
 "Heroes of Glory"){kind=icon}
 "Enigmata"){kind=icon}
 "Sugar, sugar 3"){kind=icon}
 "Civilizations Wars"){kind=icon}
 "The Light Temple"){kind=icon}
 "Epic War VI"){kind=icon}
 "Wrestle Jump"){kind=icon}
 "You Find Yourself In A Room"){kind=icon}
 "Balloon in a Wasteland"){kind=icon}
 "A Dance of Fire and Ice"){kind=icon}
 "Castle Wars 2"){kind=icon}
 "Magnetized"){kind=icon}
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 "Dead Metal"){kind=icon}
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Thank you for the feedback. :)