This mod was made with MCreator, so do not expect someting super proffesional, it is functional.
This mod is a collection of blocks from various versions of Minecraft, brought over to version 1.12.2.
In addition to the above, it includes a few interesting ideas I had for blocks, which I think might be worth considering.
Some function much like their vanilla counterparts, while others are purely decorative.
The blocks were chosen based on how much I personally wanted them in 1.12.2.
Backported Blocks:
-> Moss (1.17): Works very similar to vanilla, it converts surrounding blocks into moss if right-clicked with bonemeal. It can also be multipied using a dispenser with bonemeal from avobe.
- Due to a limitation in MCreator, the only slot of the dispenser that work to multiply the moss is the first one. The other 8 are ignored.
- It will attempt to convert to moss the blocks in a 5x5 grid centered in the original block.
-> Mud (1.19): If you right-click a dirt block holding a water bottle in your hand, it will be converted into mud, just like on vanilla 1.19.
- If you place iron bars underneath a mud block, it will start dripping water from beneath the bars, and it will eventually turn into clay, just like in vanilla as if you were using a pointed dripstone.

-> Packed mud (1.19).
-> Mud bricks (1.19).
-> Polished calcite (26.4): It can be crafted from calcite if you have the Deeper Depths Mod.
-> Calcite bricks (26.4): It can be crafted from calcite if you have the Deeper Depths Mod.
-> Calcite Pillar (26.4): It can be crafted from calcite if you have the Deeper Depths Mod.
-> Packed ice bricks (26.4).
-> Chiseled packed ice (26.4).
Original blocks:
-> Amethyst bricks: Decorative block that can be crafted with the blocks from Deeper Depths Mod.
-> Polished amethyst: Decorative block that can be crafted with the blocks from Deeper Depths Mod. It is beacon base.
Some original extra crafting recipes.

This mod was designed to be played in a cool modpack i made, the Vanilla+ Backport Pack, check it out.
Don't expect a huge amount of content to be backported over.
I hope you enjoy it and find it useful!
Credits & Disclaimer
• Code & License: Created by Saturnino9007. All original code and custom assets in 'Backports n Stuff' are licensed under All Rights Reserved (ARR).
• Official Assets: Select textures and visual assets included in this mod are the intellectual property of Mojang Studios and are used solely for non-commercial, in-game compatibility purposes.
• Disclaimer: NOT AN OFFICIAL MINECRAFT PRODUCT. NOT APPROVED BY OR ASSOCIATED WITH MOJANG OR MICROSOFT.
(work in progress)