Gonna say when they confronted the Helix king. But then after that, everything seemed to go at a weird pace, going really slow in the first half of the episode, and then all of a sudden, racing towards the finish in the end, which resulted in suddenly half the team dying in the last 5 min. of episode 24.
Best said the second half felt rushed, but at the same time, while watching the episodes, it fell like it was too lax.
Battle with Lord Genome was the real climax.