Ok this is how to reproduce the crash:
1) Start the game, play as maxwell.
2) Wear a life giving amulet, get some 10+ obsidian coconades in your inventory and a torch.
3) Spawn in the sealnado.
4) Light as many obsidian coconades as you can, before the first one explodes.
The very first obsidian conconade will kill you in 5 secs, but because you are wearing an amulet you will be resurrected soon after. Sealnado will then use his AOE attack and suck all the rest of the obsidian conconade (some are light and some aren't). The resulting explosion may or may not kill it. If it is still alive, repeat step 2~4. When Sealnado die the game crash.
Edit: Looks like the game can crash even before Sealnado die to the obsidian coconade. In anycase, I have the crash recorded.
See description