User blog comment:AlthaBlade/The Newbie's Guide To Bloons TD Battles/@comment-3153244-20140602072648

It would also sometimes be helpful to save up a little before Round 8 comes - if your opponent only has a weak tower, such as a Bionic Boomer, and is sending waves of non-stop economy bloons at you, you might be able to beat him with a huge Yellow rush (Regen or no Regen, your choice). However, if they have a Riccochet or Cluster Bomb, it won't work.

Target priorities sometimes help a lot too.