Assassin commanders with alternative win conditions usually care about dealing combat damage, so anything that makes creatures unblockable is worth considering, starting with Rogue's Passage
Tragoedia is special summoned from your hand whenever you take battle damage and gains 600 attack and defense for every card you have in your hand
"Once each turn" is a bit of an annoying limit, but in just two turns you'll have enough to pay for Strefan's ability, making it worth the downside
If the double-faced card is put into a hidden zone (your hand or library), use the substitute card again
Thankfully, with a little guidance, budding Duelists can be well on their way to crafting their perfect Deck
7 Golbat Genetic Apex (Mewtwo Packs) This Golbat card by Tomokazu Komiya features an abstract illustration of the bat-like Pokmon in a cave