mtg you may play the top card of your library Augur Autumn [Innistrad: Midnight Hunt Prerelease Promos] Top 10 Cards That Play

Thraximundar [Best Table-Wide Sacrifice Pressure and Commander Damage] Thraximundar punishes every opponent by forcing sacrifices while growing into a lethal Zombie threat that ends games through commander damage

To solve You control seven or more lands

If there are no other creatures in play, do I have to return Double Header to my hand

Delirium Whenever this creature attacks for the first time each turn, if there are four or more card types among cards in your graveyard, untap target creature

This is called the legend rule. Planeswalker cards used to have a slightly different uniqueness rule: 306.4

Power level wise the card fits in just right in Modern, as there are a lot of threats which go under the card, and cards like Veil of Summer and Cavern of Souls give slower creature/combo decks enough counterplay against it