I had tried to make a RPG Maker clone for a project of my own many years ago. (using Delphi 5 or 7) I had even made a near exact clone of Dragon Quest 1 (with a reenactment cutscene of the battle taking place at "destroyed the town of Hawkness") with semi-accurate battle stats too. So I got to work with and get a feel for the autotile system. Actually I took at a lot of inspiration from that engine.

Super Vegeta's system is a pretty good one. Covers all cases and is compressed to the point of no overhead of assets. Fading from one tile pattern to the next is a challenge and makes graphics content a bit heavier the number of terrain or pattern combinations.

If you are looking to reduce the number of pre-drawn tiles that you need, you could try using a transparency mask that is designed to fade one tile pattern over another. Essentially you'd be drawing in alpha. Not an easy task, but I'm sure there are tutorials out there. The trick is to make an alpha fade pattern that isn't a linear gradient, but a bit nosier and at the same time seamless with each other alpha fade tile.