While Taniwha is phased OUT and lands are phased IN:
- Destroy all non-land permanents
- Return all non-land permanents to their owners hand
- Cast some mad non-land permanents

While Taniwha is phased IN and lands are phased OUT:
- Use mana rocks
- Tap all land prior to phasing out (during upkeep)
- Return all lands to their owners hand
- Attack for great glory. Or just wait for the rebuild.

Use recursion to bring back things (instants, sorceries, artifacts) from the graveyard when you can.

Aim is to rebuild from a board wipe ASAP because either Taniwha is still there OR your lands are still there, so you can cast things more easily.