ok got last badge in level 31. its not so hard anymore with most upgrades. heres what to do:
get almost all towers u need before upgrading and get every mana spot in the map, get balistas (2 to 4 should do it, depending on map) at the entrypoints, hunters den on the way and near your gems (4 are enough on most maps), get a lot of chill towers (i think had about 6 to 8 on hard maps) and one mana tower, then get two red towers wherever they fit best (near the gems where ninjas reappear). i get about 10 towers before upgrading the first.
i needed almost all skills. u get a LOT of mana with description above and you can get more gold by cutting trees, so u always have money for upgrading all the towers. be sure to save mana before ninja waves but i always had enough to bomb even other waves. hope this helps
like it, but i think achieving brilliant should bring more XP, first two rows are not that hard, but in the last 5 its so much luck depending on freeze/fear. also HOTKEYS!!