you would need to either use our modpack or play with pixelmon reforged and forge launcher
https://www.technicpack.net/modpack/ultimate-reallife-roleplay.616349 this is the link to downloading the modpack
However, if you want to play with forge:
Forge
Pixelmon Mod
you download these two^
afterwards, if using forge, you would need to move your pixelmon mod to your mods folder. to do so:
if you are on
Windows,
1) Press Win + R
2) Type in %appdata%
3) Go to .minecraft/mods
4) Drag the downloaded Mod into the mods folder
5) Restart your Minecraft
if you are on
Mac,
1) Open finder
2) Go to help at the top left
3) Open the library folder
4) Go to ~/Library/Application Support/Minecraft/mods
5) Drag the downloaded Mod into the mods folder
6) Restart your Minecraft
after all that, you should be good to go