Terastodon, Woodfall Primus, and Primeval Titan are probably the best cards for the "big green creature" role, but Simic Sky Swallower and Broodmate Dragon can serve the role as well, although they require greater deck manipulation to be able to hard cast should you draw either of them before finding your Natural Order
There will always be a correct one for your deck, so its hard to fit one on this list
Aristocrats, spellslinger, tribal, voltron, group hug, stax, and more
If you are new to Lorcana, the starter decks are complete decks that come with a paper playmat, a basic rulebook, and some tokens
You also have the choice to just put it back in the command zone, which you might want to do if Grenzos not around