For example,
SandSquirt.
During the Komodo Scale quest, Serge can kill it with a heavy attak (do about 15 damage).
Komodo Pup and
Beach Bum both have less HP than it is listed in the Encycopedia or, Ultimania. Perhaps they have only half of that amount.
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Edit*
After I recruited Poshul, their HP became normal.
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Edit*
So perhaps when there's only Serge in party, enemy's HP will be halved?
Some situation that can be tested: Mama Komodo battle, Radius Battle(lecture), Time Devourer battle in new game+, home/another world regular battles before anyone joins in.
I've tested that Mama Komodo has only 76 HP (half of its normal value), Radius has 30000HP as usual.