Planeswalkers aren't creatures, so they can't attack or block. However, planeswalkers can be attacked (directly and indirectly via the redirect of non-combat damage from the player to the planeswalker).
508.1a The active player chooses which creatures that he or she controls, if any, will attack. The chosen creatures must be untapped, and each one must either have haste or have been controlled by the active player continuously since the turn began.
509.1a The defending player chooses which creatures that he or she controls, if any, will block. The chosen creatures must be untapped. For each of the chosen creatures, the defending player chooses one creature for it to block that's attacking him, her, or a planeswalker he or she controls.
Can a Planeswalker block? Specifically, Xenagos, the Reveler? The 2014 rulebook says yes, but I read what I thought was a WoC blog and the guy said no.
Are you refering to this line from the basic rule book: "Your planeswalkers can be attacked by your opponent’s creatures (if so, you can block as normal)"?
If that is what you are talking about, this is refering to the fact that you are still able to block your opponents creatures with your creatures even though they are attacking a planeswalker you control instead of you.
Your opponent can choose to attack your planeswalker or ignore it and directly attack you.
In that sense you can't block with a planeswalker.
Private Mod Note
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712.5b The controller of another player can't make choices or decisions for that player that aren't called for by the rules or by any objects. The controller also can't make any choices or decisions for the player that would be called for by the tournament rules.
Example: The player who's being controlled still chooses whether he or she leaves to visit the restroom, trades a card to someone else, agrees to an intentional draw, or calls a judge about an error or infraction.
My own rules when building a Commander deck:
1) Underrated general that I can build around but the deck must work without him/her too.
2) Every card must be legal in both banlists.
3) No infinite combo that could win (and ruin) instantly a multiplayer game.
4) Synergy at all costs; stay on theme, avoid goodstuff.