When this card declares an attack: You can target 1 face-up Spell Card your opponent controls; destroy it, and if you do, inflict 500 damage to your opponent. If you have no cards in your hand, except the turn this card was sent to the Graveyard: You can banish this card and 1 "Destiny HERO" monster from your Graveyard; draw 2 cards. You can only use this effect of "Destiny HERO - Celestial" once per turn.
Since it's attack can be pretty low in comparison to many commonly used level 4 monsters, you can increase its attack by using skills that give you the field spells, or bringing them in the deck. Joey's exclusive skill "Fields of the Warriors" gives you Sogen at the start of the duel, and Aster's skill "Destiny Calling" is for Dark City when your LP is at 3000 or lower.
To the grave
A good way of sending Celestial to the grave is to use him as fusion material for cards like Destiny HERO - Dangerous, or use Mask Change to special summon cards like Masked HERO Anki. You can then use Celestial's effect from the grave to get some resources back. You can also use Destiny Draw to draw 2 new cards out of your deck, and then during your next turn draw 2 more cards with Celestial's effect.
So. I just had a match against D heros at dlvl 20. I had a Drystan face up, Glory facedown. He triggers Destiny Calling, summoned Celestial, I chained and went for Destiny. Drystan effect activates, chose celest to pop. Didn't pop. I was like, mkay. He attacked, popped my destiny, re-attached it, drystan activates, chose celestial, didn't pop, again! He went for game. Now can someone explain that shit to me..
Turn 1: set Solemn Scolding, summon Drystan. Turn 2. Summons Drilldark, activate Scolding. Turn 3, set Glory, attack, turn 4, first post. Those where all the cards in play. Don't have a replay, crap. But that's what happened.
By paying a couple of dollars of real money. (You can only get 1 copy via Gems.) That being said, the second copy of the deck is pretty cheap. (It's the only money I've actually spent on Duel Links so far.)