Always declare Machine-type with Array of Revealing Light so that Vellian's monsters cannot attack the turn they are summoned.
Since Vellian's monsters cannot attack immediately, Guardian Statue and Medusa Worm will allow you to control the board by removing your opponent's monsters from the field when they are flipped.
Remember to always use their effects to flip them back face-down for reuse next turn.
Only have 2 Guardian Statue/Medusa Worm on the field at most. Reserve one of your monster zones for Gravekeeper's Vassal.
Sometimes Vellian will have more monsters than you can remove with your Guardian Statues and Medusa Worms, in this situation use Acidic Downpour or System Down to remove all Machine-type monsters from the field.
Before your final turn, make sure you either normal summon Gravekeeper's Vassal or tribute summon Mystical Beast of Serket while Temple of the Kings is on your field.
Send Mystical Beast of Serket and Temple of the Kings to the graveyard to special summon Blue-Eyes Ultimate Dragon
Remember to use Anti-Magic Arrows during your final battle phase to avoid Vellian's Zero Gravity.
Immediately Summon Gate Guardian by tributing the monsters you get from Elements Unite. Gete Guardian should be in DEF position first unless Crowler will attack you with his monster equipping Ancient Gear Tank.
The next thing you need now is to activate at least 1 healing card so that Crowler does not burn you to death with Ancient Gear Tank. Once you regain enough LP, it's better to switch the position of Gate Guardian to ATK.
Lastly, you need to equip Gate Guardian with at least 2 Horn of Unicorn so that Crowler cant overpower your monster, both in attack and defense position.
After that its now only a matter of getting to zero cards quicker. Use Shard of Greed for extra draw power. The combo of Gravekeeper's Recruiter and Wonder Wand to get 3 cards out of your deck. It is best to search out another Gravekeeper's Recruiter if possible to reuse the combo.
Remember to use Anti-Magic Arrows at the start of your final battle phase.
If anyone is wondering whether 'Elements Unite' is worth using, it sure is! Here is one with which I had 75% success rate yesterday:
1x Gravekeeper's Vassal
1x Antimagic arrows
1x Dian Keto the cure master
2x Union Attack
3x Supremacy Berry
2x Noble Arms - Caliburn
1x Card Advance
1x Pot of Benevolence
1x Secret Pass to the treasures
3x Spikeshield with Chain
3x Jars of greed
1x Windstorm of Etaqua
The key 2 cards you want in your backrow are 1 spikeshield and 1 spikeshield/caliburn. Always start with Guardian in defense and keep him like that until you get your first healing spell. You only need to destroy 2 of his monsters for Benevolence to recycle them, then if you have Spikeshield just switch in defense mode until you have the union combo. Don't forget to activate anti-magic arrows on last turn.
What's crazy is after I beat him 15x with this deck yesterday I didn't receive a SINGLE Gear Knight or Golem. Today after duelling him 5x at level 10, not worrying about max score he finally drops a freaking Gear Knight!
All you need is to have lower life points than Corwler the turn before you win(Your Turn, then Crowler, again your turn and win), you can use any card to lower your points, heal Crowler, pay a cost etc.
does the elements unite deck have high chance of winning?
nope eu deck is terrible, if you draw your healing he'll summon a 3600 atk gear golem and destroy your unbuffed golem, if you get your draw he'll tribute someone with the equip spell and do 600 damage, litterally 5% win rate at best
admitedly i've only tried once but the standard dark paladin deck for bastion also worked for crowler
If you can just be more honest and tell us it's YOU who's having a problem unlocking crowler, then I would have gladly helped you. Since you're so bent with preserving your image and reputation which doesn't even matter in this site where there's anonymity, I have to pass up on your question so you can learn one bit.
Since this "community" is so bent with critisizing others, I wouldn't admit anything to be honest.
To sorrel, I don't know which are the missions for unlocking him. But it's usually just playing around. For comeback victory, just use a pvp or beater deck, get some damage and then win