first of all i will start with explaining what "sabotaging" means, how it can be done with a game that does not have friendly fire and the best legion to use for this

sabotaging your teammate is making him lose even when he tries, this is not a thing that you should do in games but since you can already just be AFK i dont mind showing you some good tricks so its more fun to do

how can you sabotage your teammate? for example a good way to sabotage your teammates in a game such as CSGO is to shoot them and deal friendly damage but this isnt a thing in this game so you (me) have to get a little creative in order to do that

the best legion to use in order to sabotage your teammate by far is definitely the blue legion so you want to have a deck with blue color if you want to annoy your teammates though other legions are usable too

blue just has so many cards which can be used to sabotage your teammate/help the opponents!
here is a list of all of them.

relocate: you can relocate the fragile backline ranged units to the front which in most cases they will die quick and this will make your teammate's mana go to waste

inverse gravity: its a good way to inflict self root on your own (and your teammate's) units which sometimes can give your opponents advantage in battle

factory reset: you can use this card on all (non legendary) units and buildings, what it does is restoring the health and status of 8 units in an AOE to their original values (the way unit is when you just summon it) which means you can both restore opposing tanks to full hp and remove buffs from your own units. keep in mind that this card is expansive and you cant use it twice on the same unit

and last but not least, aegis IX: it's ability "orbital drop" kills all non legendary units in a small aoe, and that thing includes friendly units

here are pictures of these cards (by order) in case you are new to the game

so your deck is going to be blue and X, and as you know we always got to find what X is so i will talk about all the things that other legions can offer (without giving images because i am too lazy) to ruin the match

black legion: in this legion you can use frostworm spawners to fill the spawner slots quickly with a unit that is bad at being a spawner, soul maelstrom to banish friendly units while also dealing damage to them, tyrus to place on top of an enemy wave making it grow even bigger and kind of situational you got deep freeze in case the opponents use something with a lot of hp but low armor so that making it heavy armor actually helps them (such as a fully buffed oracle which has light armor and does not care about losing 300 hp)


green legion: in this legion you got wisp spawner which is bad for the same reasons of frostworm (stage 1 fragile single unit with a bad range), entangling roots and sapling bushes and sapling charge and brratu can all be used for the purpose of making the opposing wave grow larger, though keep in mind that your teammate might kill the opposing units when they are busy killing all the stuff


white legion: you can use footmen/priest/balista spawners according to your opponents to help delaying them and making them have bigger waves though these spawners are probably not as bad as frostworm and wisp, besides these pretty much the only other thing you can do is using light pulse to stun your opponents and helping them grow but this is not optimal


blue legion: i already covered it but maybe breacher spawner spam can help ¯\_(ツ)_/¯


and finally crystal legion: in most matchups you can use granite scouts spawners to let your opponents build bigger waves and block slots for your teammate but this isnt a really good legion for that but because you can always run crystal its not a problem, you can also run petrify to basically freeze your own units for 12 secs and even heal opposing units and buildings with it so its really great for this

these are all the cards and tactics you can use in order to sabotage your teammate in crystal clash. in case i missed something you can do please comment and let me know
i hoped you enjoyed reading my guide and also hope you will not use it to annoy players in game (please dont)