Fortress

[silver-knee]

Adds the possibillity for a fortress island as one of the island_subtype_raffle. Fortresses are also independently available for future use on diffrent islands.

On the fortress island, the silo is protected by hostile turrets, worms, walls, gates and nests.
There are also independent fortresses that protect high value loot.

The fortress island's difficulty is depending on the distance from the start. The fortresses get more layers, turrets use better ammo and worms get bigger. But there are also more independent fortresses with loot at later stages.

This is the silo fortress at the minimal level:

This is the silo fortress with some additional fortresses at the maximum level.

[danielmartin0]

When I evaluated this last year, I did so in the context of a 'biter fortress island'. But as a minor upgrade to the difficulty of later islands, this is an interesting concept. Will revisit.