It turns every single creature on the battlefield into target creature you control, legendary or not
Whether evoke's sacrifice ability triggers when the creature enters the battlefield depends on whether the spell's controller chose to pay the evoke cost, not whether they actually paid it (if it was reduced or otherwise altered by another ability, for example)
When you do, return target creature card with mana value X from your graveyard to the battlefield with a corpse counter on it
Changed Urgent Possession
If eight or more mana was spent to cast that spell, sacrifice Tellah and it deals that much damage to each opponent
(f) If the lot's failure to conform to its Authorship Warranty can only be shown by a scientific process which, on the date we published the Authorship description, was not available or generally accepted for use, or which was unreasonably expensive or impractical, or which was likely to have damaged the lot