For speed IV achievment: Mk-1-F body, Mk-V-MW fins, Mk-V-F engine, Mk-V boosters, forsage engine and cooling system. From the start just use boosters at all times. Took me 2 tries until nothing was in my way and was about 5 seconds into it. Good luck.
In a sense it is more simplistic than other TD games, yet that's the main reason i find it so enjoyable, other TD games have way to many options and most it's just stack of money and max towers where as this it takes exp to level which is a good change.
That's what makes it challenging, the fact you have to buy when you can as much as you can, if they made it one button to get all you can, well you'd have such an excess how could you lose?
 "Cursed Treasure 2"){kind=icon}
 "Strike Force Heroes 2"){kind=icon}
 "Caribbean Admiral"){kind=icon}
 "Tesla Defense"){kind=icon}
 "Into Space 2"){kind=icon}
 "NoNoSparks: The Ark"){kind=icon}
 "Swords & Potions"){kind=icon}
 "Endless War 5"){kind=icon}
 "Dawn of the Dragons"){kind=icon}
 "Upgrade Complete 2"){kind=icon}
 "Villainous"){kind=icon}
 "Cursed Treasure: Don't Touch My Gems!"){kind=icon}
 "High Tea"){kind=icon}
 "Sonny 2"){kind=icon}
 "Protector IV"){kind=icon}
 "Belial Chapter 2"){kind=icon}
 "Bloons Tower Defense 4"){kind=icon}
 "Ultimate Assassin 2"){kind=icon}