Apologies for the long wait for this, it fell off my radar with wrangling other projects.
Update 1.5 addresses the overly easy endgame with a host of balance tweaks and new challenges.

• Energy drained faster on more difficult islands
• Watcher is sometimes accompanied by TWO Hunters instead of one
• The final Watcher is particularly tricky, reach the end of a campaign to find out why ;)
• Upgrades repriced to use XP, so you can't grind early levels to upgrade any more
• Memory stones grant you a point of XP to spend on upgrades
• Memory stones now non-interactive for 2 seconds, to make accidental draining less likely
• Another attempt to fix the pesky floating tree, shout if you see it in this build!