Browsing the forums, I´ve seen many game-breaking combinations, involving use and/ or abuse of supplemental books. Is there a topic for core- only madness? I´ve searched in Google and the forums, but didn´t find anything.
Here you go. This is where we tried to make Pun Pun using core only rules (and came close to succeeding). Enjoy! 
Thank you very much :D
The "Planar Bind an Efreeti and demand infinite wishes" abuse is core.
The "Planar Bind an Efreeti and demand infinite wishes" abuse is core.
That's an awesome idea
Candle of invocation shenannigins are core as well.
Infinite HD with Awaken cheese and unlimited clones are both Core too.
Infinite HD with Awaken cheese and unlimited clones are both Core too.
What´s that? :$
-Awaken cheese: Get a servant of yours (maybe your Simulacrum or whatever) to use infinite wishes to cast Polymorph any object and Awaken repeteadly on you. You gain 2 HD every time. Eventually this amounts to virtually infinite feats, skill ranks, hit points, attack bonus, saves, ability scores and whatnot.
-Infinite clones: Shapechange into a Shambling mound and then launch a series (preferably thousands) of self-recharging electrical traps to shoot at you. Gain nigh-infinite constitution due to Shambling mound's special ability. Shapechange into a Black pudding, notice how your hitpoints remain the same due to the wonky Polymorph rules that require subsequent changes. Then have a few dozen archers shoot at you and you gain a little friend every time. Dismiss Shapechange, repeat ad nauseaum.