The Z-Mech's primary weapon is the Robo Laser. The Robo Laser overheats if fired for too long. When it is overheated, the weapon cannot be fired for a few seconds. Once it has cooled down, it can be fired again.
Plants getting too close for comfort? Good thing you're in a giant robot with huge metal feet.
Strategies
With
As the Z-Mech, you are still vulnerable to crowd control attacks such as Goop or Time Snare. These abilities can disable your own abilities, rendering your firepower almost useless. While your Z-Mech is powerful, it's a dangerous risk to go head on against a large group of plants. You will likely be outnumbered and vanquished very quickly if you charge into a group of plants. Instead, if you find a group of plants huddled together, try using Missile Madness. This powerful ability can deal heavy damage to targets caught by the missiles or in the blast radius. Alternatively, stay within a group of your teammates and help them pressure groups of plants with your massive damage and health. The Z-Mech's Stomp ability deals a good 75 points of damage and hits in a small radius.
Once the time to eject comes, if you have a Gravity Grenade ready, you can throw it down on to the self destructing mech to pull nearby plants into the explosion (Works for all Imp Z-Mechs).
Against
Against the Z-Mech, shoot the glass as it will deal normal damage to the mech. Rose can ignore the Z-Mech's resistance boost and can damage it normally. Peashooters can use Pea Gatling to quickly destroy the mech.
The best class to go against the Imp is his arch-nemesis Citron, also from the future. The EMPeach is most effective against mechs rather than other classes, so use this to your advantage to attack the mech while it is stunned. If you're using Frozen Citron, you can use EMPeach to stun the mech and freeze it for an easy vanquish. When Imp is at low health, use the Spin Dash to vanquish him. Make sure to be wary using the Ball Form near Imps as his Gravity Grenade will leave you unable to counterattack.
Tips and tricks
Keep in mind that while you are calling your Z-Mech, you are immune to damage as soon as the beam of light appears, and shows the Z-Mech health until the Z-Mech is deployed.
When in your Z-Mech, don't rush into a group of plants, as they can team up on you and take you out very quickly.
A good tactic to do if your Z-Mech is ready is to wait until the Imp has low health. Once you call in the Z-Mech, you will automatically get full health.
If you call your mech in a zero gravity zone, then eject from it in an area with gravity, your Imp will be able to jump higher (as if he were still in a low gravity area).