My mistake, Darkamber! I will fix that right now.

Thunder (Thick Fat, Immunity)
HP: 95
Energy: 88
Speed: 26
Boosts/Drops: 0
Status: Badly poisoned.
Actions: Screech~Giga Impact~Metronome

Cetus (Marvel Scale)
HP: 85
Energy: 83
Speed: 81
Boosts/Drops: 0
Status: Fine
Actions: Hypnosis until it hits, then Rain Dance and if you have time, Scald 'em!
Round two starts with Cetus trying to hypnotise her opponent, but she can't maintain eye contact long enough for it to work. Thunder responds by Screeching loudly, but it seems that Cetus manages to cover her ears and block out the sound (how the hell does Screech miss?!). She goes for a second Hypnosis now, and this time she manages to put Thunder to sleep for one action, meaning his misses his attempt to Giga Impact, though he does now wake up, just in time to see a rainstorm brewing overhead, thanks to Cetus' influence. How will this affect the battle? Oh crap. Snorlax is wiggling his finger back and forth, and it's not an offensive gesture... Suddenly, his foot is aflame, and he kicks Cetus with mighty force! What a shame she resists it... And it's raining.
Calcs:

Thunder (Thick Fat, Immunity)
HP: 95
Energy: 66
Speed: 26
Boosts/Drops: 0
Status: Badly poisoned.

Cetus (Marvel Scale)
HP: 78
Energy: 50
Speed: 81
Boosts/Drops: 0
Status: Fine
Rain for five rounds.