Okay, After reviewing all the titles of all the Final battles of all the previous leagues listed below, I can come to the following conclusion.
1) This is not the final episode for the sinnoh league. In all the final episode of the previous leagues, they all have words like "End, Final, and Last" in there title.
2) If this is not the final episode for the league, then there could only be two posible senario:
a) Ash vs LT in this episode. This battle will not be sweep. It will last for at least 2 episode because there will be at least 1 more episode for the sinnoh league.
b) LT will verse someone else and Ash will be watching. The battle should last no more than 10 mins, because they will need the other 10 mins to set some sort of rivalry/friendship with LT and Ash. This battle will determine how strong the LT is.
Regardless of whether it will be A or B, whenever Ash vs LT, it will bound to be an interesting battle.
Previous League's final episode:
Indigo League:
"Friends to the End" (Pokémon League! Final Battle!)
"Pokemon Rīgu! Saigo no Tatakai!" (ポケモンリーグ! さいごのたたかい!)
Orange League:
"Enter The Dragonite" (Final Battle! Kairyuu Appears!!)
"Fainaru Batoru! Kairyū Tōjō!!" (ファイナルバトル！カイリューとうじょう!!)
Johto League:
"Johto Photo Finish" (To the End of the Destiny Battle! Respective Way!)
"Furu Batoru no Hate ni! Sorezore no Michi!!" (フルバトルのはてに！それぞれのみち!!)
Hoen League:
"At the End of the Fray" (The Last Fierce Fighting! The Road to the Championship!!)
"Saigo no Gekitō! Yūshō e no Michi!!" (最後の激闘！優勝への道!!)
Battle Front Tier:
"Pace - The Final Frontier!" (Deciding Battle! VS Regice!!)
"Kessen! VS Rejiaisu!!" (決戦！VSレジアイス!!)
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With LT vs Ash, I believe the following pokemon will be the best fit for the battle.
Heracross
Attack: Sleep talk, Hyperbeam, Mega Horn, and Focus Punch.
Heracross can counter darkrai’s dark void with Sleep talk, and attach with x 2 super effective bug and fighting type move. Hyperbeam is just there to match it’s strength with darkrai’s Kamehameha in the images.
Snorlack
Attack: Snore, Icepunch, Focus Punch, and Body slam
A pokemon that love sleep. One might think that he’ll learn to snore or sleep talk by not to compensate for it sleeping some time in battle. Again, snore will counter sleep talk, and focus punch will do super effective damage.
Staraptor
Attack: Quick attack, Close combat, Brave bird, Steel wing.
It’s combine speed with quick attack will help it dodge a few dark void. Close combat will be able to do some super effect damage.
Inferape
Attack: Flarebiz, Flame Thrower, Much Punch, Sky uppercut
Again, it’s fighting move can do some major damage to Darkrai.
Pikachu
Attack: Volt tackle, Thunderbot, Iron Tail, Thunder.
The writers can boost pikachu’s level back to level 99999999999999999999 and have it kick some *** with power electric attack.
Chariard
Attack: Sesmic toss, Flame Thrower, Dragon Breath, Steel wing.
Sesmic toss will be deadly to darkrai because it’s weak against fighting type. Steel wing show be strong enough to use as a defensive move to block any of darkrai’s attack.
All these pokemon at designed to take on Darkrai, but because of the type and attach variety, they can also help take on the rest of LT’s other 5 pokemon as well.
