Pennywise appearing in Japanese fanarts is usually a "Pennywise Recommends" (shitty option X) meme.

Meme usually goes by inserting Pennywise and the rainy storm drain scene into another series, with him recommending a shitty option to another character. The standard response is "You won't fool me (again)!"/"You can't fool me."

The original meme had him recommending a shitty movie called "5-Headed Shark Attack".

Quoting myself a few years ago:

NNescio said in post #3252344:

I think I figured out how this meme got started.

Originally it popped up on Niconico video as a joke subtitle version of the infamous scene in the original 1990 series (the first one likely being this, recommending a shitty movie [5 Headed Shark Attack]) that spawned a whole series of "Pennywise recommends" imitators.

Then recently somebody had the 'bright' idea of taking the meme and adapting it to FGO, with Pennywise acting as a metaphorical (well, probably literal too) devil tempting the player into rolling the gacha (Pennywise recommends [CHARACTER X]). The popularity of the meme then exploded even further.