If you fail to keep a monster at bay: inescapable death as it runs into your hitbox and slowly whittles away at your hp, while your swing can't reach it...
Here's how to beat the two last levels with a brilliant rating: build only maxed crypts with all fear and freeze upgrades at the entrances and spam meteors. That is all.
This worked for me for every level, including survival: on each side, a sleeper/perfume block on the bottom, and 4 cannons on top, all facing inward. This creates a deadly pit of concentrated fire. Very few demons make it even to the toys, and those can be killed in melee. If there are ghosts in the level, an eye block can be placed in the middle. In survival, just replace what gets destroyed and gather souls to increase melee damage. No problems.
Build only triangles, wait until you get Small Ships, then spam those. Instant win recipe. I didn't even once use any other ship and beat all 3 difficulties this way.
After getting the wings, in the area south of the gate, is a section where you have to jump from crumbling platform to crumbling platform, which is actually impossible. I can't jump diagonally except down-left and up-right.
Sometimes, the gun starts to lag really bad and jitters randomly, making it impossible to play. This happens regardless of quality and my computer isn't slow either.
The controls feel very clunky. I often died because the character continued moving for a while after I stopped pressing the button. Jumps are a tad short/low. Also, the hit box seems to not match the character? Sometimes I survived touching spikes, sometimes I died while clearly not doing so.
 "Starcom"){kind=icon}
 "Heroes Empire"){kind=icon}
 "Legend of Pandora"){kind=icon}
 "Legacy of a Thousand Suns"){kind=icon}
 "You Are The Road - Molyjam 2012"){kind=icon}
 "New Star Soccer"){kind=icon}
 "Cursed Treasure: Don't Touch My Gems!"){kind=icon}
 "Demons Took My Daughter"){kind=icon}
 "XenoSquad"){kind=icon}
 "The Competitor"){kind=icon}
 "Fat Warrior 2"){kind=icon}
 "Aliens Kidnapped Betty"){kind=icon}
 "Sierra 7"){kind=icon}
 "Aurora"){kind=icon}
 "Ultimate Gamer Challenge"){kind=icon}
 "Topsy Turvy"){kind=icon}
 "Tealy & Orangey"){kind=icon}
 "Champions of chaos"){kind=icon}