Im not and have never been an MTG judge, but you can sit back and enjoy this summary of how to use the level up mechanic (insert Super Mushroom sound)
If youve played against them once, youve played against them all because the small differences in iteration between anyones list for these decks can be so minute youd feel like youre playing against a stock list
But if you change this with something like Opalescence (or are using the Faceless One), then your background commander would be affected and could be targeted by anything that says commander creature. Most of the cards that refer to commander creatures instead of just commanders are background cards themselves
Even if the curser doesnt then wipe all the now measly minions from the cursees board, it becomes so much easier for anyone else at the table to destroy them, not to mention just attacking
If a card says loses all abilities (like Darksteel Mutation or Sudden Spoiling), that permanent still keeps any +1/+1 counters, loyalty counters, shield counters, or other counters already on it