Complex sentence: The Forgotten One is the strongest known Eternal through his own dicipline and his strength and senses had been enhanced by "The One Beyond All" before he fought Thor and the Eternals during the 50 year judgment of the Celestials.
Split into simpler sentences: The Forgotten One is the strongest known Eternal through his own dicipline. His strength and senses had been enhanced by "The One Beyond All" before he fought Thor and the Eternals during the 50 year judgment of the Celestials.