If Gideon becomes a creature the same turn he enters the battlefield, you can't attack with him or use any of his {T} abilities (if he gains any).
Gideon of the Trials
Gideon's second ability causes him to become a creature with the creature types Human and Soldier. He remains a planeswalker with the planeswalker type Gideon. (He also retains any other card types or subtypes he may have had.) Each subtype is correlated to the proper card type: planeswalker is only a type (not a creature type), and Human and Soldier are just creature types (not planeswalker types).
No game effect can cause you to lose the game or cause any opponent to win the game while Gideon's emblem is in effect. It doesn't matter whether you have 0 or less life, you're forced to draw a card while your library is empty, you have ten or more poison counters, you're at your Glorious End, your opponent casts a second Approach of the Second Sun, or so on. You keep playing.
Magic: The Gathering · ™ & © Wizards of the Coast · Illus. Terese Nielsen
Card data via Scryfall. Rarix is fan-made; not endorsed by the rights holders.
