MTG: EDH / Commander

Oskars ability still has you pay the cost of the spell. So the value isn't in casting more spells. The value is in essentially nullifying all discard costs of activated abilities (since they're now beneficial rather than detriments), and that the spells can be cast at any time, essentially giving everything Flash.

Therefore, I'd suggest removing the cards that benefits from casting lots of spells, like cards with storm. Replacing them with sorceries and permanents that are particularly useful if you can Flash them out, like combat tricks, or permanents that effectively get haste because you could play them on the previous turn. for example:

• instant-speed board wipes (like the toxic deluge you have in there).
• creatures that can be flashed out as blockers eg with deathtouch, or Stuffy Doll, or Grotesque hybrid
• mind control (instant gain control of opponent A's creatures to block opponent B's creatures).

You could also include some global stax that is made one-sided by your commander. Like Oppression.