The Water Portal

Mining in Minecraft is great. Exploring caves is even better. But, when you've forgot the way out, are swarmed by mobs, and have practically no way out, that's when you use a Water Portal. A Water Portal is a small circle made from Powered Prismarine, which can be crafted from any Prismarine block, plus a Nautilus Shell and Guardian's laser energy-collected by a water bottle by leading the Guardian onto land and collecting the laser's energy into a bottle. The Powered Prismarine Blocks have to be activated by placing one Heart of The Sea item into a frame, then filling the frame up with water. Once activated, the portal will change color every few seconds. You'll need to build another nearby, just without the Heart of The Sea, but on the other side a certain Marine-found item in a frame, same with the other portal. Then you can jump/dive into the portal, and be transported to the corresponding portal. This idea would be a great time saver for miners, and even save player's lives. Only Marine-based mobs can follow, as well as Zombies, however. 

Thankyou! Please vote for this, as this is my first idea, and feel free to comment constructively!