Overview: This is a very relaxing build, as the build only needs four towers in all; you can set up your main offense very quickly, leaving you to do whatever you want while you wait (be it AFK, or just mess around with the extra TP). It's also a stress-free build in terms of TP; you will not have to worry about not having enough TP to keep buffing your towers.
This build is also really good for collecting gold and drops, as all monsters will be killed in concentrated areas.
This build does not work very well with ninjas because their Wood Rush skill won't stop much with only one Freeze tower. A slightly modified version of this build works much better for ninjas (demo'd here).
Hit the jump for detailed tactics.
Tactic:
Set up the first three towers and max the TP buff ASAP. It's not necessary to kill the monsters at the 2x area.
Prioritize on the first Gaia tower, keeping the Freeze tower and the second Gaia close behind. At this point you can probably AFK for ten minutes or so.
Once the first Gaia is maxed, start focusing on the second Gaia until it's maxed.
At around stage 37, start stalling the monsters while you work on getting the Freeze tower to level 10. You can still AFK up til probably stage 42 or something but you will have to let the monsters make a full lap around the map, which is at the expense of your completion time. If you start stalling now you can still kill the whole waves at the spawn point. So it's up to you what you prioritize.
The first Gaia tower should now start getting buffed from here onward. One buff will be sufficient until probably Stage 46-47.
Get the final tower started. Upgrade it to level 8, being careful not to overspend on TP because you will need to buff the first two Gaia towers.
At stage 44, both Gaia towers on the first row now need to be buffed from here onward.
Stage 45-48: if the wave of monsters take the lap around the map with at least/more than half HP left, re-buff one or two of the Gaias once they start coming in from the north.
Stage 49: Buff every tower.
And here is Stage 50 in action:
During this final wave of monsters it's important to separate the monsters into packs (seen at 1:15). If there are too many monsters stacked, some will slip through the Gaias unharmed. I delayed myself at doing this properly because of trying to take screenshots and I left a huge stack of monsters near the tail of the wave (1:33). Once that wave reached the Gaias many of them slipped right past (2:13), so the stone took a good amount of hits but the run was still completed.
