This Puzzle uses various sized grids to fit sets of pentominos within. I’ve chosen a 9×9 grid. I think the name, Ripple Effect is suggestive of bigger integers making a bigger splash given their unneighborliness in the rule set. There are no tip sheets as yet, although a strategy may be like that of Paint By Numbers, where you have to account for not only where candidate numbers could be, but also where they cannot be. Ripple Effect was created by Nikoli in 1998.
There are some sites with Ripple Effect Puzzles:
You Play.com, an online puzzle site with free and paid memberships. Getting a free membership is a chore, if not impossible. The form decided my email address was already in use and rejected its association with a new userid! Clicking on Account details made no impression on the script.
Online Puzzle Ripple Effect has multiple puzzles of sizes 8 x 8, 10 x 10, 18 x 10 and 24 x 14.
Ewe Weidemann’s Sudoku Variants Page.
This site has a huge number of Sudoku and other Puzzle variants well organized, although mostly one example of each kind.
I may have to acquire some Nikoli published puzzle books on this variant.