Infect and pw

[Rass]

What happens if I attack a pw with a creature with infect.

What happens if I block an animated pw say  {Sarkhan, the Dragonspeaker} with  {Phyrexian Crusader}.

[redwolv]

Atacking you will just remove loyalty from the pw like normal.

Blocking a animated one is different. Your infect will put -1/-1s on the walker.these -1/-1 conters wikk stay on them one they are back to being pw and not creatures. This means of he turns into a creature again he will once again be affected by the -1/-1 counters. Plus if you can give them enough -1/-1 counters they will can die like a normal indestuctable creature which has suffered from -1/-1 spells/counters

[Remillo]

An important difference to note here between Sarkhan and the Gideon ones is that Sarkhan stops being a planeswalker when he becomes a creature.  Damage will be dealt to it as it's a creature, so Infect and WIther will put -1/-1 counters on him and he wont lose any loyalty.  Now, if you animate a Gideon and use something like Skull Crack or Leyline of Punishment, things get funny.

8/25/2015: If damage that can't be prevented is dealt to Gideon after his first ability has resolved, 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.

Blocking a Gideon with a Phyrexian Crusader while damage can't be prevented would cause him to get two -1/-1 counters AND lose two loyalty counters.