Credit to Nathaniel Zimmerman for creating this addon, I only helped him to post it here

Small warning
Sometimes when holding a mech spawn egg or Spawner in the main hand because it have a high pixel texture it might lag so quickly spawn the mech or change to into something else in the hotbar to negate the lag spikes

Anyway with that out of the way I will present you with the addon explanation
To first start you need to create a mechanical anvil 

and iron plate which here is how to make them
 

Mechanical anvil Recipe :

Iron plate recipe :

After crafting mechanical anvil and iron plate you can craft any mech you want and here is the 
 

Tooless mech

A very basic mech with no tools (as it name implies) 
Health :100
Speed : 0.3
Ability : jump
Spawner recipe:

Miner mech

a drill equipped mech
Health :100
Speed : 0.3
Ability : jump, destroying block (stone materials, sand, and gravel) 
Spawner recipe:

Lumberjack mech

a saw equipped mech
Health :100
Speed : 0.3
Ability : jump, destroying block (wood materials) 
Spawner recipe:

To make armed mech you need a mech laser 
And the recipe for mech laser:

Battle mech

A more Armored mech and equipped with a gun
Health :200
Speed : 0.25
Ability : jump and automatically target and shoot monster
Spawner recipe:

Atst walker

A star wars inspired mech slightly weaker than battle mech but also slightly faster
Health : 150
Speed : 0.3
Ability : jump, automatically target and shoot monster
Spawner recipe:

Atat walker

A star wars inspired mech very tanky but also very slow
Health : 350
Speed : 0.2
Ability : automatically target and shoot monster and can carry 7 rider or player 
Spawner recipe:

Tronbike

The fastest vehicle but also very weak
Health : 50
Speed : 0.6
Ability : n/a
Spawner recipe:

To make antigravity speeder you need antigravity crystals cluster which can be found on the end and cluster will drop crystals

Speeder

An antigravity speeder, slightly stronger  but also slightly lower than speeder bike
Health : 85
Speed : 0.4
Ability : doesn't affected by gravity (can float) and can carry 2 player or rider
Spawner recipe:

Speeder Bike

An antigravity speeder bike, slightly weaker but also slightly faster than speeder
Health : 70
Speed : 0.5
Ability : doesn't affected by gravity (can float)
Spawner recipe:

Remember to turn on experimental holiday features and upcoming features to make the add-on work