"Requires 3 Tributes to Normal Summon (cannot be Normal Set). This card's Normal Summon cannot be negated. When Normal Summoned, cards and effects cannot be activated.
Cannot be targeted by Spells, Traps, or card effects. During the End Phase, if this card was Special Summoned: Send it to the Graveyard. You can Tribute 2 monsters; destroy all monsters your opponent controls. This card cannot declare an attack the turn this effect is activated."
Mirror Force does not target so he can be destroyed by it.
As for Ra make sure you pick the Non-Anime version if you want to play a real duel with it. There are 3 in the game the first two can be used in normal games and are just different images the third one is Anime only.