Maniacal Laugh can easily turn the tide of the battle, or even potentially let you win the game. Using this on strong zombies can obliterate your opponent's defenses, and using it on weaker ones can make them quite formidable as well. However, since this trick is very expensive, you shouldn't waste it on a weakling unless you need it to save yourself. Rather, it is optimal to use it on one of the recommended zombies below.
Examples of zombies that form powerful combos with it are:
Any zombie with the Strikethrough trait, as it has a higher likelihood of activating its Frenzy trait due to it also being able to hit a frail plant behind a tanky one. Only Template:PvZHLink can do this normally.
Any zombie with the Anti-Hero trait to allow it to plow through a plant in its way and hit your opponent for extra damage. Only Brain Freeze can do this normally.
Any zombie with an ability that gives it lots of strength, such as Template:PvZH Link or Template:PvZHLink.
Any zombie who needs to survive or take damage to be formidable, such as Jester or Template:PvZHLink.
Any zombie with the Bullseye trait, as its high strength will most likely tear through the plants and deal massive damage to the opponent without charging up their Super-Block meter. If this is done on either Shieldcrusher Viking or Wizard Gargantuar, the game can end within two turns unless they heal or Soul Patch is on the field. Only Immorticia can do this normally.
Paparazzi Zombie, as his ability gives him a small boost on top of the Maniacal Laugh boost. Only Immorticia can use this normally.
Nurse Gargantuar to strengthen his ability, resulting in 18 health healed if he successfully destroys one plant on his lane and then hits your opponent, and 20 if there are two plants.
Zombies with the Frenzy trait like Smashing Gargantuar and Vimpire are better left alone from this trick unless you think the huge stat boost is worth it for them, as they already have the the Frenzy trait by default, and the zombies above may be more favorable to get the Frenzy trait.
If you are playing as The Smash, you could also consider Coffee Zombie instead, if giving the Frenzy trait to all your zombies is what you really want, but Manical Laugh could still serve as a great game ender in a deck that utilizes Frenzy.
Against
If you see your opponent saving 6 brains or more for tricks, and there are no threatening plants on the field that may otherwise tempt them to play Locust Swarm or Hail-a-Copter (against Immorticia only normally), it is likely that Maniacal Laugh is about to be played. In that case, you can play Brainana to take away their brains, or try to destroy the zombies on the field before they become a huge threat.
Wall-Knight can use Uncrackable to avoid taking damage, allowing you to stall and avoid taking damage, although you will not be able to predict this trick being played on the current turn unless you block and get it. Using tricks or fighters that allow you to Freeze zombies, such as Template:PvZHLink or Template:PvZHLink can also stall a zombie boosted from Maniacal Laugh for a turn or more. Ideally, Root Wall or Template:PvZH Link can also be used if a plant is in the same lane as the boosted zombie.
Smarty heroes can use cards with the Bounce effect, such as Template:PvZHLink, as bouncing that zombie removes both its huge stat boost and its extra Frenzy trait. As a last resort, you can play Shamrocket, Template:PvZHLink, or Template:PvZHLink to destroy that zombie, but for the latter, see if any of your key plants get destroyed from it first. Also, all these can only be done if you can survive the Fight! phase since zombie tricks happen after plants get to play.
Gallery
Plants vs. Zombies Wiki has a gallery for Maniacal Laugh.
Beastly class. It costs 6
to play, and its ability gives a selected zombie +5
/+5
and the 
Frenzy trait.
/+5
Freeze zombies, such as Template:PvZHLink or Template:PvZHLink can also stall a zombie boosted from Maniacal Laugh for a turn or more. Ideally, Root Wall or Template:PvZH Link can also be used if a plant is in the same lane as the boosted zombie.
Brainy
Crazy
Hearty
Sneaky