Gyruda, Doom of Depths (also known as Gigan, Cyberclaw Terror) has already made an impact in several formats, such as the Legacy Gyruda deck that has already proven itself. A similar combo application is available in Standard, using Spark Double and various effects that flicker Gyruda in and out of the battlefield to repeat the trigger.
Bant Gyruda Combo (Standard)
1 Gyruda, Doom of Depths 4 Humble Naturalist 2 Aether Gust 3 End-Raze Forerunners 4 Charming Prince 4 Growth Spiral 4 Thassa, Deep-Dwelling 4 Spark Double 4 Paradise Druid 3 Gyruda, Doom of Depths 1 Temple of Plenty 4 Island (335) 4 Fabled Passage 1 Temple of Enlightenment 5 Forest (347) 1 Plains (331) 4 Temple Garden 4 Temple of Mystery 4 Hallowed Fountain
The companion mechanic is seemingly going to take over Standard (and possibly more formats) for the forseeable future, as the benefit of starting the game with a guaranteed extra card far outweighs the meager deckbuilding restrictions that they impose. This is especially true for Gyruda, since it allows you to build a combo deck based around a game-ending effect that you never have to worry about not finding.
Unlike older formats, in Standard the only Clone effect that we have access to is Spark Double. Luckily, this is the best one of the bunch since it lets us flood the battlefield with copies of our Legendary creature, often just winning the game through an unfair accumulation of advantage triggers. Charming Prince and Thassa, Deep-Dwelling bridge the gap to be able to get us more repeated Gyruda triggers and accumulate a game-winning advantage (or an outright win if we mill our opponents out entirely).
End-Raze Forerunners is our way to close the game, being a great reanimation target if you have cluttered the battlefield with large bodies and just need to complete the formality of killing your opponent. Aether Gust is a spicy piece of tech for this deck. It has been a powerful enough card to maindeck in Standard for the last several months, but in this deck it has a little extra utility: it can permanently deal with a troublesome permanent in response to your own Gyruda trigger (and even give you access to it if it was a creature), and in some weird spots it may be able to add a random green creature on top of your own deck so that your opponent mills out before you.
In similar fashion to the Legacy version of the deck, after our combo pieces we just need fast mana to get to our guaranteed six-drop. Growth Spiral and Paradise Druid and known staples in Standard, and Humble Naturalist from Ikoria gives us a critical mass of two-mana acceleration spells, completely negating the downside of not being able to play odd-costing cards.