Alpha Metallurgical Resources (AMR) had the lowest return in 2019 by a mid-cap US stock, returning -86.1%.

ASSET	YEAR	% RETURN
Alpha Metallurgical Resources (AMR)	2019	-86.07%
Cogent Biosciences (COGT)	2019	-83.33%
Liquidia Technologies (LQDA)	2019	-80.26%
CleanSpark (CLSK)	2019	-73.25%
ChronoScale (CHRN)	2019	-68.72%
Peabody Energy (BTU)	2019	-66.8%
Amneal Pharmaceuticals, Inc Class A Common Stock (AMRX)	2019	-63.84%
Indivior PLC Ordinary Shares (INDV)	2019	-63.74%
Kinetik (KNTK)	2019	-62.47%
Trevi Therapeutics (TRVI)	2019	-60.53%
Kiniksa Pharmaceuticals (KNSA)	2019	-59.83%
Custom Truck One Source (CTOS)	2019	-58.88%
Bitfarms (KEEL)	2019	-57.79%
BioCryst Pharmaceuticals (BCRX)	2019	-56.27%
Celcuity LLC (CELC)	2019	-54.45%
GameStop (GME)	2019	-49.51%
BBVA Banco Frances SA ADR (BBAR)	2019	-49.26%
Pampa Energia SA ADR (PAM)	2019	-48.37%
Transportadora de Gas del Sur SA ADR (TGS)	2019	-47.57%
OceanaGold (OGC)	2019	-46.89%
Ideaya Biosciences (IDYA)	2019	-46.43%
Central Puerto (CEPU)	2019	-45.32%
Merit Medical Systems (MMSI)	2019	-43.11%
Resideo Technologies (REZI)	2019	-41.14%
Scholar Rock (SRRK)	2019	-40.98%

Mid-cap stocks are treated as having a market cap between $2B and $10B.