Since it seems near impossible to find the good Game Maker Sonic engines I've made this post and hosted many of the engines on my own site to provide easy access to anyone looking for engines.
Sonic Dash/Xmas Engine
The best engine for GM period. Very smooth and lots of features.
Dash/Xmas was created by Damizean & RougeYoshi and are provided free for use.
Sonic Dash Current(Recommended)
This is the most current form of the Dash includes monitors, shields, parallax, dipping bridges, rings, springs, Sonic, Knuckles, and Tails with S3&K moves and following partner.
Xmas Gift Engine
Similar to the the above engine only less advanced. This engine includes: rings, monitors, parallax, shields, Sonic, Knuckles, and Tails with S3&K moves and following partner.
Sonic Dash Old Engine
This is a very old version of Sonic Dash which has some bugs. I recommend not using this version. That said there are many gimmicks included in this version which can be ported to a newer version without to much trouble. I won't mention them all because there are a lot but its enough to say that it consists of a whole zone which can be played through so everything one would need to do so can be found here even a boss.
Sonic Revival Engine
Sonic Revival Engine Thread
The Sonic Revival Engine 2.0 (Mirror)
This engine was made on top of one of Dami's older engines and is created by Chaos Rush. It has shields, Sonic, Knuckles and Tails and a few other things. Its less advanced then Dash but some may say its easier to use if you don't understand states machines.
Kain's Sonic Engines
Kain's Online Showcase Engines Page
S3&K GM Engine (Mirror)
This is Kain's attempt at a Sonic 3 engine there's a lot of stuff here including spikes, monitors, shields, rings, badniks, and more defiantly worth a look.
cGM Engine (Mirror)
Kain's newest attempt at a Sonic engine has spikes, monitors, rings, Sonic, Knuckles, and Tails, and more. However it is missing a few things such as jump through platforms.
I made mirrors to a few things without permission and if anyone get's mad I'll take them down. I have done this because engines have been known to go MIA and I do not want that to happen anymore. Thanks to everyone that made these great engines. Thanks to DMAshura and RougeYoshi for helping me get all these engines.
Sonic REX Engine
Sonic REX Engine Thread
The Sonic Revival Engine 2.0 (Mirror)
This engine was made on top of one of Dami's older engines similar to the Sonic Revival Engine and is created by Sponick. It probably has more features than any of the other engines including, zoom tubes, swings, moving platforms, Sonic and Tails with Sonic 3 moves, spikes, shields (sonic 3), springs, star posts, 8 way and rotating direction both, and some stuff I'm probably missing. Its really quite a complete engine.
Grid Spatia Indexing (GSI)
GSI is a system made by Damizean that allows you to take objects delete them when they off screen and not in use. GSI is similar to the built in GameMaker deactivation but is much more efficient and can increase performance of your game much more than using GameMaker's deactivation alone. You will find that using GSI is a necessity as levels get bigger and full of more objects that they slow down your game on even some reasonably powered machines. I've included the latest version of GSI along with a example on how to use it below. If you have any questions feel free to ask me (Overbound) as using GSI can be a bit tricky. Keep in mind are if you are using GSI on an object be sure you are not also deactivating it with GameMaker's built in deactivation feature. Second only use GSI on objects that do not move as it detects objects by their coordinates and moving an object makes GSI think it needs to create a new one. Third as GSI deletes objects and then creates them as the come on screen release that the creation code will run again and any variables set before the deactivation will not be saved.
Grid Spatial Indexing 0.15
At the very least you should consider using GSI I know from personal experience that it can increase game speeds by more than 20 FPS.
Damizeans Hydrocity Style 3D Water Example
Just what the title says its a really neat effect. Thanks Dami!
Damizean 3D Water Example