As a very general rule for Limited, I would look to play something like this: 1 mana: 02 creatures 2 mana: 46 creatures 3 mana: 35 creatures 4 mana: 4 creatures 5 mana: 3 creatures 6+ mana: 12 creatures That's far from hard and fast, but it's a good place to start
Or probably your deck minus one card, which includes a Force of Negation and a way to kill them on your next turn
UA11_XR 3 Artifact 3, ocT: Target player removes a card in their graveyard from the game
A lot of your cards will be able to crew this and so yeah, it is just an overly good card that fits neatly into this archetype
The play pattern goes like this: you cast Taniwha and pass turn, then on your next turn you untap and Taniwha phases out, then on your next turn Taniwha phases back in and your lands phase out, on your next turn Taniwha phases back out and your lands phase in, etc