On one hand, Jan Jansen can be tapped to sacrifice an artifact creature in order to create two treasure tokens
The 5/5 Zombie Warrior costs six converted mana and has an ability that gives each creature card in your graveyard unearth for three converted mana
The magic happens with Ashlings second ability, whenever you sacrifice a nontoken Elemental, she creates a hasty token copy of it
Last week I looked at Commanders here: ( This is not X Spells themselves but the support infrastructure to make them work...ready
Kinnan, Bonder Prodigy supercharges every mana-producing creature and artifact, which powers its secondary ability to dig for giant creatures and put them into play for free
Gut deals damage fast, turning spare Treasures or expendable creatures into 4/1 hasty menace tokens, hitting as early as turn 3