Do the metamagic from Eldritch Corruption and/or Spellscale blood quickening count as "known" for the following feats: Accelerate Metamagic, Practical Metamagic, Heroic Metamagic, Metamagic Spell Trigger, Midnight Metamagic? Now this is interesting because you can gain extra use out of feats that you can't strictly use because you didn't meditate for them or you exceeded the usage limit on (like sudden metamagic).
Now Eldritch Corruption says you gain the effect of the metamagic (enlarge, extend, heighten, widen) on a spell at your allies' expense, so it seems doubtful but you are already delving into the morass of taint rules so your DM might be somewhat permissive.
Now Spellscales certainly know metamagic (empower, heighten, silent, still, widen) that doesn't fulfill prerequisites, but they may not be able to use them on a particular day.
Metamagic Spell Trigger is the feat with the most wide scale usability, followed by Heroic Metamagic and Midnight Metamagic, all the others require you to pick one feat to apply.
Another feat in similar vein is Cerebremetamagic(dragon).
