Complex sentence: When Red Skull is dying due to his imperfect Super Soldier Serum, he teams up with MODOK who upgrades HYDRA's tech from A.I.M. to kidnap Captain America.
Split into simpler sentences: When Red Skull is dying due to his imperfect Super Soldier Serum, he teams up with MODOK. Modok upgrades HYDRA's tech from A.I.M. to kidnap Captain America.