Copied from another thread:
For the Tower Defense mode I was thinking of Co-op and Versus modes. In Co-op it is your team of five against set waves (or Endless/Unlimited Waves if you set that as a variable - like Hardcore mode) where you construct towers to defend against each wave. In versus it is 2 teams of 5 each fighting to defend against the other teams waves of minions while trying to push their own. The towers will be necessary. Without them there are too many minions to fight. You do need to fight some minions to get the currency needed to build the towers (most likely shards) but it is impossible to fight off all the minions without the towers. The better you do against the minions though the better towers you can afford to build.
Tower ideas? Different projectile types. Single target projectiles. Single target projectiles (or energy beams) that chain to other targets. Single target projectiles that branch out/split to multiple targets. Projectiles that cause AoE damage upon impact. Towers cause damage or create an effect in an area around them (PBAoE).
Different firing modes. Single shot. Burst fire. Full auto fire. Sustained beam.
Different ranges. Sniping range. Long range. Mid range. Short range. ‘Melee’ range.
Different damage types and/or effects. Damage. DoT. Slow. Stun. Knockup. Push. Blind. Root. Pull. Extra damage to shields. Extra damage to health. Shield piercing.
Shielded towers. Minion spawners (x type). Minions spawners (mixed type). Minion spawners (elite type). Hero spawner (AI/bot Battleborn with skin that makes them look like a robotic/Minion Corp version of the original - skin unlockable for players in game through x challenge).
Everyone starts with several tower types they can build (perhaps 5 types of towers out of 10 or 15 available starter towers randomized for each player). More kinds of towers can be built as blueprints are found. Loadouts can be created and selected before each match. More powerful towers will cost more shards to build.
Amidst the level there will also be the standard buildables such as the turrets, supply depots, accelerators, and drone spawning points.
The objective is to survive until you have passed every wave in the standard game mode (or as long as you can in the endless wave mode).