“Ojamuscle” is considered to be an “Ojama” card, so you can send it from your hand to the Graveyard for the cost of the first effect. If you control “Ojamuscle” and it is a monster (for example, with “Magical Hats”), it is considered an “Ojama” monster for the second effect.
If you send an "Ojama" monster from your hand to the Graveyard, then you can target the sent monster to Special Summon it. However, you cannot activate this effect of "Ojama Country" if you have no "Ojama" monster in your Graveyard.
If a monster has its ATK and DEF switched by "Ojama Country" and is then affected by "Inverse Universe", then its ATK and DEF are switched again. Afterwards, if "Ojama Country" is removed from the field or if there are no longer any face-up "Ojama" monsters on the field, then the ATK and DEF switched by "Inverse Universe" do not change.