Power of the Tributed When you sucessfully Tributed Summon "The Winged of Ra", its ATK will becomes the sum of the ATK of the Tirbuted Monsters, and its DEF will becomes the sum of the Tributed Monsters.
If you summon Destiny HERO - Plasma to take control of Blowback Dragon, you will still need to use defensive spell/trap against his Barrel Dragon since he can still get over your Plasma using his spell/trap cards.
Use the lower level monsters and keep destroying keith's monsters. Don't attack if he has a face-down trap since it could be rare-metalmoprh. Set a magnetic mosquito if you think he will tribute summon either blowback or barrel dragon. Use acid raid if you don't have mosquito to destroy his tribute monsters. It's best to summon BEUD during second to last turn to avoid it getting destroyed early. On the last turn, summon vassal and use the union attack combo.
Summon either the hunter or jerry and destroy keith's monsters when they are in defense position to not lower his LP. If they are summoned in attack position, switch it to defense using otohime on the next turn. Acid raid if their attack is higher than yours, or mirror wall to defend as well as reducing your LP. Lower your LP to more than half of keith's LP and keep destroying his monsters so the BEUD can get a direct attack to deal 10,000 damage after equipped with sword of deep-seated.
Since the ATK of Twin-Barrel Dragon is 1700 and same to that of Axe Raider, the highest ATK level 4 monster you can get, you need to use equips spells or other ATK boost cards to get your monsters to defeat the dragon.
Use Spell/Trap removals
Destroying Keith's Machine Conversion Factory, Second Coin Toss, and Rare Metalmorph is important to help your monsters to beat Keith's Machine monsters.
This is the easiest way to farm keith (7k to 8k) depending on the bonus rewards
Skill : Mythic depths
This skill is essential to lower his monsters attack.
2x Vorse raider
3x Alien shocktrooper
1x Dunames dark witch
(You can use any 1900+ ATK monsters)
3x Chain destruction
(This is your bread and butter card use it to get rid of all twin-barrel dragons in his deck which is the most annoying card)
(to boos your attack in case he used his rare metalmorph)
1x mirror wall
2x pot of benevolence
1x gift of the martyr
1x secret pass
1x big koala
1x des kangaro
1x master of OZ
All you have to do is get rid of his twin-barrel dragon, keep attacking his monsters to prevent him from tribute summon and gg.