To get brilliant on the last two levels is impossible. For the penultimate level, the mana pool needs to be taken over instantly, you need luck that the first two waves don't touch a gem at the last second, you need mana bottle drops, and in the middling waves, a cook or bard boosting a diver, even when played perfectly, will reach a gem. This is also all done with max upgrades and during daytime, not even nighttime with massively restricted tower placement. THEN there's the first smuggler and the goddamn monkey and it's impossible to get past them without somebody grabbing a gem.