"Dash [cost]" means "You may cast this card by paying [cost] rather than its mana cost," "If this spell's dash cost was paid, return the permanent this spell becomes to its owner's hand at the beginning of the next end step," and "As long as this permanent's dash cost was paid, it has haste." If you choose to pay the dash cost rather than the mana cost, you're still casting the spell
However, with limited numbers of essential cards like 004-018-mirabel-madrigal-gift-of-the-family and 004-013-julieta-madrigal-excellent-cook, the deck really isnt a strong choice in terms of overall power
Sin's last ability puts all counters that were on Sin onto the target creature, not just its +1/+1 counters
Similarly, if you make an opponent the protector of a Siege you control, mana symbols in that battle's mana cost count toward your devotion
It gets extra flavor points for actually winning with dragons