The term "mono team" refers to a single element team. Once you have collected enough monsters to put together a team of all the same element, the amount of damage you are able to do will greatly increase.
One of the best things you can add to a mono team is swaps. Swap and Element-Swap are active abilities that will change gems to the element of the monster casting the ability. Swap changes hearts and Element-Swap changes gems of the element weak against the of the monster.
Adding swaps to your team will give you the opportunity to make larger combos. You will be able to make damage combos on turns you may have no previously had any matching gems.
Another advantage is an increase in speed and that is very important for time based matches. Combos of gems of elements not on your team will simply take a moment to move on to the attack of the opponent. Getting more moves in during a timed match means more damage.View a Mono Team
Zodiacs matchups are not easy when you first start playing, but once you get enough mobs and start trading, it will benefit your team for a number of reasons. Firstly, passive abilities will be unlocked. For example, let's look at the strongest attack passive in the game, Rogue. At level 1, Rogue takes away 10% health, but adds 65% to your monster's attack. If your monster has an attack of 1000, then with this bonus the attack is now 1650(wow!). At Rogue level 5, the attack is now increased by 105%, which would put your monster's attack at 2050(even more wow!).
Another advantage of matching zodiacs is zodiac specialization. It is free to unlock your first zodiac. The second is 50g, the third is 100g, and then every unlock after is 150g. I recommend only unlocking one, maybe two if you end up with much better mobs in another zodiac. You should only concentrate on one. When you unlock a specialization, all monsters you have with that zodiac get a boost to all of their stats. At level 1, the bonus is 0.5%. That may not seem like a lot, but once you get it leveled up, it can give you quite the advantage. For example, level 50 adds a bonus of 25% to all the stats of the monsters you are using of that zodiac.