Using Lava Lobber Achievement
Last map, Eye of the Storm, is best to use this achievement. Survive until the with some Labbers intact, and then try and bunch up the last couple of waves where they go all out and send in loads and loads of heroes. Don't play to complete the level or protect too much of the gold. Play to get the achievement.
You can get BoneHead Achievement on "hold the line". Set up your defenses as normal, with an extra barricade down one of the back paths. Keep throwing in skeletons as you can... You should have 25 with no problem.
Protect Mana Hints
Protect your mana crystals by placing them in locations where the pesky heroes cannot reach them.
Thieves are capable of destroying spiked floors, so keep an eye out for them and take them out with other means.