So, in terms of its in-game mechanics, what does Dark End Dragon actually do
Whenever this creature enters or attacks, exile up to two target cards from graveyards
They copy themselves for each spell cast before it, so it's possible to cast enough spells to burn all your opponents with Grapeshot, or mill them all with Brain Freeze if you're able to cast a ton of spells in one turn (made easier with the Hullbreaker Horror combo)

TRR 86 1 Boss's Orders RCL 154 1 Pokmon Fan Club UPR 133 1 Pokmon Nurse EX 145 2 Pok Ball SUM 125 2 Switch SVI 194 2 Ultra Ball BRS 150 1 Rare Candy SUM 129 1 Super Rod BKT 149 1 VS Seeker PHF 109 1 Sun Seed CLV 27 2 Computer Search BS 71 Energy - 16 8 Basic Grass Energy CLF GRA 6 Basic Fighting Energy CLF FIG 2 Double Colorless Energy BS 96 Visual Card Breakdown Venusaur Deck Set List Bulbasaur (Base Set) Ivysaur (Base Set) Venusaur (Base Set) Paras (FireRed & LeafGreen) Parasect (Supreme Victors) Scyther (Jungle) Pinsir (Sun & Moon) Sandshrew (Unbroken Bonds) Sandslash (Unbroken Bonds) Onix (Lost Thunder) Hitmonlee (Sword & Shield) Hitmonchan (Sword & Shield) Doduo (BREAKthrough) Dodrio (Undaunted) Chansey (Base Set) Snorlax (Rebel Clash) Lugia ex (Pokmon TCG Classic) Bill (HeartGold & SoulSilver) Boss's Orders (Rebel Clash) Computer Search (Base Set) Pok Ball (Sun & Moon) Pokmon Fan Club (Ultra Prism) Pokmon Nurse (Expedition) Professor Oak (Base Set) Rare Candy (Sun & Moon) Rocket's Admin

If you dont have Mana Echoes out, you can achieve the same effect with Sliver Queen, Cloudshredder Sliver, Gemhide Sliver, and Training Grounds on the battlefield
even the humble Fiend Hunter can bust through a stalled board state