When you think of a tower defence game, what usually comes to mind is a long, winding path, with various build spots situated around it. As you defeat enemies, you earn more money to place units on these spots, and they will automatically attack any enemies that come within range.
However, while that might be the most common kind of tower defence game, there are plenty of other types as well. A popular example would be Plants vs. Zombies - instead of one path it has five, all of which allow you to place units on them. Even though these paths are right next to each other, units on one path won't cover the paths next to them, they'll only fire forward on their own area.
Monster Combine TD seems to be heavily inspired by this game, and features almost exactly the same basic setup. The plot is fairly odd - you are transported into an alternate dimension where you have to defend a magic school from its own students, who are attacking it with armies of monsters.
While it seems quite similar to Plants vs. Zombies, it does have some major differences. In order to defeat the enemy armies you'll have to conjure up your own monsters to counter them; this is done using a deck of cards, which can be selected before each level begins. The idea is that you place your cards on summoning circles to spawn basic units, as well as special items, which can then be used to transform those basic units into more advanced creatures that fill various roles, such as a short-range attacker, a long-range attacker, or one that shields units behind it.
Unlike the plants in PvZ, this game's units are not rooted to the ground, meaning they can also be freely moved around; this quickly becomes very important. Almost every level features various types of terrain, from some sort of sludge that makes you move slower to hot springs that slowly restore the health of any unit standing on them. As such you'll be moving your units around a lot, in order to make the weakened ones retreat or move them into a better position. There's also a magic attack you can select beforehand, which can be along the lines of a lightning attack that hits all enemies or an attack boost for all your units, and can be used a limited amount of times in each stage.
While the gameplay of getting cards and using them to summon monsters - and then upgrading them - might seem cool, there are some severe drawbacks to this system. The cards you receive are completely random, so for the most part you'll be at the mercy of luck, and the game barely gives you any time to get things sorted out before it starts sending the first enemies at you. When you use cards - or if you shuffle the ones you have - there's also a decent wait before you'll actually get your new cards, which eats away at the limited setup time you have even more. Therefore it's not uncommon to spend several times resetting a stage before you can even get past the first few waves.
As you clear stages you'll receive experience that can be used to rank up certain stats, such as the maximum amount of cards your deck can have or the time it takes for the magic spell to become usable, but these improve so incredibly slowly that it will take a long time before you'll notice any difference.
While the game has some moderately appealing graphics, the rest of the presentation seems to be a bit lacking - the music is quite repetitive, and there's an inordinate number of spelling and grammar mistakes in the text.
Monster Combine TD is an interesting take on the tower defence genre, building off of the gameplay of Plants vs. Zombies, but the inherent flaws in some of its gameplay aspects will quickly come to light and put a damper on the experience. If you're fine with resetting a lot you might be able to find some enjoyment in this game, but otherwise you'll quickly get annoyed and look elsewhere for your tower defence needs.