She starts as a puny 1/1, but with enough attacks, she'll provide a tasty buff to your life and her own power
Susan Foreman makes an excellent Doctors companion, coming down on Turn 2, and if your mana works out, you can cast The Fifth Doctor on Turn 3

Scientists Academy Elite Adventurer's Airship Agna Qel'a Arcade Gannon Archive Haunt Artful Looter Assassin Gauntlet Atlantean Skirmisher Bag Check Bag of Holding Baron Strucker, HYDRA Overlord Bellowing Crier Benthic Biomancer Bloodfire Mentor Bonded Fetch Boosted Sloop Broadside Barrage Cait, Cage Brawler Canyon Crab Captain of Umbar Carlo, Suave Schemer Ceta Sanctuary Chakra Meditation Change of Plans Civilized Scholar Collector's Vault Conqueror's Foothold Copycrook Coralhelm Chronicler Currency Converter Customs Depot Cyclonus, the Saboteur Daily Bugle Newspaper Data Scrubber Deal Broker Deny Entry Desolate Lighthouse Diviner of Fates Doc Ock's Henchmen Doctor Doom, King of Latveria Dragonborn Looter Dreadwing Scavenger Echo Inspector Elite Instructor Emet-Selch, Unsundered Enclave Cryptologist Erratic Visionary Evangel of Synthesis Evie Frye Facet Reader Failed Inspection Flying Drone Frontline Sage Furtive Analyst Furtive Courier Geyser Leaper Goben, Gene-Splice Savant Gran-Gran Grixis Battlemage Hapless Researcher Hard Cover Harrier Strix Hypnotic Grifter Icewind Elemental Illuminator Virtuoso Improbable Alliance Inspired Sprite Jace Reawakened Jace, Cunning Castaway Jace, Vryn's Prodigy Jalum Tome

It keeps its abilities and types.) 3/3 You choose the target creature as you put Steel Seraph's triggered ability on the stack
You can also make your Celestial Colonnade or something a dork and swing later after this has triggered