Otherwise, I suggest using different methods to get your hands on cards in Arena
The main sets that have ninjas are: Kamigawa Plane Betrayers of Kamigawa Kamigawa: Neon Dynasty Modern Horizons New York City, TMNT crossover Teenage Mutant Ninja Turtles Teenage Mutant Ninja Turtles Eternal Some sets with only one or a few ninjas are: Commander 2018 Duskmourn: House of Horror Final Fantasy Commander Foundations Jumpstart March of the Machine Outlaws of Thunder Junction (OTJ) and the Commander set (OTC) Planechase 2012 Unstable Wrap Up Thousand-Faced Shadow | Illustration by Ekaterina Burmak Learn the way of the shinobi and youll be a master of stealth and subterfuge
Berta, Wise Extrapolator Clement, the Worrywort Flubs, the Fool Genghis Frog Glarb, Calamity's Augur Gorma, the Gullet Grolnok, the Omnivore Helga, Skittish Seer Thalia and The Gitrog Monster The Gitrog Monster The Gitrog, Ravenous Ride Uurg, Spawn of Turg Venus, Torn Between Worlds Yargle and Multani Yargle, Glutton of Urborg
For 6 mana, you can probably play much better dragons like Lathliss, Dragon Queen, but Oros has a nifty triggered ability if it deals combat damage to an opponent
From there, you can tap down as many creatures on your opponents side with Kytheon's Irregulars as youd like without running out of mana
[Fire] Spirit Burner 10+ Discard the top 5 cards of your deck