Crypt Champion
Creature — Zombie
Double strike
When Crypt Champion enters the battlefield, each player puts a creature card with converted mana cost 3 or less from their graveyard onto the battlefield.
When Crypt Champion enters the battlefield, sacrifice it unless 
was spent to cast it.
Illustrated by
RNA Guild Kit#53UncommonEnglishLegality
Rulings
The first triggered ability isn’t targeted, so the creature cards aren’t chosen until the ability resolves. Each player chooses which creature card from their own graveyard to return. If a player doesn’t have an applicable creature card, that player does nothing. If a player does have any applicable cards, that player must return one to the battlefield.
If this enters the battlefield in a way other than announcing it as a spell, then the appropriate mana can’t have been paid, and you’ll have to sacrifice it.