Gideon Blackblade — ruling 1

If an effect causes Gideon to lose all abilities during your turn, he's still a Human Soldier creature and a Gideon planeswalker. This is because his first ability applies before that ability is lost.

Gideon Blackblade — ruling 2

If an Equipment becomes attached to Gideon while he's a creature, it'll become unattached during the next upkeep that isn't yours. The same is true of any Auras that become attached to Gideon that can't enchant a noncreature planeswalker.

Gideon Blackblade — ruling 3

Any counters that are put on Gideon remain on him while he's not a creature, even if they have no effect on a noncreature planeswalker.

Gideon Blackblade — ruling 4

If damage that can't be prevented is dealt to Gideon during your turn, that damage will have all applicable results: specifically, the damage is marked on Gideon (since he's a creature) and that damage causes that many loyalty counters to be removed from him (since he's a planeswalker). Even though he has indestructible, if Gideon has no loyalty counters on him, he's put into his owner's graveyard.

Gideon Blackblade — ruling 5

You choose which ability the target creature gains as Gideon's first loyalty ability resolves, not as you activate it.

Gideon Blackblade : règles, fonctionnement et interactions (MTG)

Gideon Blackblade is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

During your turn, Gideon Blackblade is a 4/4 Human Soldier creature with indestructible that's still a planeswalker. Prevent all damage that would be dealt to Gideon Blackblade during your turn. +1: Up to one other target creature you control gains your choice of vigilance, lifelink, or indestructible until end of turn. −6: Exile target nonland permanent.

How it works : Gideon Blackblade

Original English text — Wizards of the Coast / Scryfall

#1May 3, 2019· Wizards of the Coast
If an effect causes Gideon to lose all abilities during your turn, he's still a Human Soldier creature and a Gideon planeswalker. This is because his first ability applies before that ability is lost.
No other card is named in this ruling.
#2May 3, 2019· Wizards of the Coast
If an Equipment becomes attached to Gideon while he's a creature, it'll become unattached during the next upkeep that isn't yours. The same is true of any Auras that become attached to Gideon that can't enchant a noncreature planeswalker.
No other card is named in this ruling.
#3May 3, 2019· Wizards of the Coast
Any counters that are put on Gideon remain on him while he's not a creature, even if they have no effect on a noncreature planeswalker.
No other card is named in this ruling.
#4May 3, 2019· Wizards of the Coast
If damage that can't be prevented is dealt to Gideon during your turn, that damage will have all applicable results: specifically, the damage is marked on Gideon (since he's a creature) and that damage causes that many loyalty counters to be removed from him (since he's a planeswalker). Even though he has indestructible, if Gideon has no loyalty counters on him, he's put into his owner's graveyard.
No other card is named in this ruling.
#5May 3, 2019· Wizards of the Coast
You choose which ability the target creature gains as Gideon's first loyalty ability resolves, not as you activate it.
No other card is named in this ruling.