Verses Mode idea
Considering the game is now multiplayer, how about a new verses mode?
Basically the idea is one player plays as normal and sets up traps, but the other player plays on the orcs side!
When the game begins the player on the orcs side will have a certain amount of money for example 10,000, Along the bottom of the screen where the trap hotkeys would normally be would be your different enemy types and there price, so for example a regular orc would cost 50 coins.
When you click an enemy type it will subtract the cost of that enemy from your total money and that enemy will enter the level and run for the rift like normal.
Something like a regular orc would be really cheap so you could spam it and send loads at once, however something more powerful like a Fire Ogre could cost more like 1,000.
So how do you earn money playing as the orcs? Every rift point you take from the other player could earn you 1,000, so if you kill the other player you will get 3,000. Also destroying barricades or killing guardians should earn you money too, maybe 100 for a barricade you destroy and 500 for every guardian you kill.
There would be a lot of strategy to this, learning the best combinations of enemies to send to give the other player the hardest time possible.
It should be 8 rounds with each round lasting 1-2 mins, if the normal player loses all there rift points then the player on the orcs side will win, however if you still have rift points at the end then the defending player wins!
Also the player on the orcs side should be able to play as one of the mobs they spawn, so for example if they pay 1000 for a frost ogre then there should be an option for the player to enter the ogre and play as him.
Please post your suggestions and if there good I'll add them to the main concept :)