RPG Insanity

I notice something when I fought serious Butler at first time he only at lvl 50, but after repeated fought him again and again he increase his power level to Max 255.

So this another infinite challenge like sinker n lapis but the difference is Max level challenge.

Note - his almost got first turn and when first turn he will unleashed skill which make all heroes left 1k hp and 2nd is attack is random. This can be resolved by using Bowen bond effect which increase all parameters at start battle.

I hope I'm right about this cause I fell strange his got stronger from the last I fought him.

No, you're right. Serious Butler will get stronger for the next fight if you agree to the challenge, if not I think you'll get the same Serious Butler's level from the previous fight during the 2nd time he asks you in the same conversation.

You can also do these in the fights against him:

Debuff him by casting All Parameters Down with a bard
Paralyse him
Attack him with skills that have "Delay Turn" effect