The way I beat Sea clan leader as Chaos mage is to have 174 mana (other values work, but differently), level 6 for the attacks and level 1 mana burn.
First, use level 6 attack.
Then, keep burning mana until the Sea mage starts their first attack.
You should have 13 mana.
Counterattack, then mana burn, then counterattack.
Finally: rest, counterattack, and repeat until done.
This method is compatible with winning every other fight. You need to finally level up mana burn when you confront the Chaos clan leader. I can beat the Sea judge of good with max level attacks and mana burn, and level 3 defences.
For some people, the only play button that works at the loading screen is in the right click menu. The loading screen stays in the background if you click it, but doesn't ruin the gameplay. This has been said many times before.
Useful fact: If you complete the game with getting all of the skills from the Roundites and no defeats from the Shadow, you would have 210 gems remaining.
My game won't leave the loading screen either, but there is one play button that works for me: Right-click and press play! The loading screen remains but it hasn't bothered me much.
Triggers would be useful. One could add them as tiles, objects or stats (e.g. timer, player stats, death count) and activate them to change something on the map. This enables more secret paths, easy path if you die a lot, change characters' text and lots of other things for the players.
 "Book of Mages: The Chaotic Period"){kind=icon}
 "Pixelo"){kind=icon}
 "Level Up!"){kind=icon}
 "Sandbox Hero"){kind=icon}