we should be able to change the order of some upgrades, for example
long range darts before piercing darts, extra range before faster shooting, glaive thrower before sonic boom, sonic boom before multi target, longer range before bigger bombs, laser vision before super range
arctic wind + tempest tornado + glue splatter = very slow bloons/globos muy lentos
moab maulers + sun god = total defense against bfbs/defensa total contra bfbs
 "endeavor"){kind=icon}
 "Bloons Tower Defense 4"){kind=icon}
 "GunBot"){kind=icon}
 "Secret Exit"){kind=icon}
 "Reincarnation: Let The Evil Times Roll"){kind=icon}
 "Toss the Turtle"){kind=icon}