This is probably related to #260. When we make status effects more arbitrary, we'll try to get rid of silly restrictions like this one.

There's a constant POWER_SHIELD=11 which is currently used for displaying the shield art. Shields should still be working, but not displayed properly if set to another index.

This will all get fixed in v0.18's work to completely revamp the buff/debuff system.

Well, I also noticed that shield no longer works without a gfx defined. So maybe what happened is that shield requires gfx to be set in order to not crash the game, and since graphics are only loaded if shield id=11, that's why the crash?

Sounds like a possibility. In that case we need some error checking to make sure we're not drawing null image pointers.

drawing null image points is checked in SDL, you can safely pass a null pointer to sdl and it will return having the SDL_ERROR() being able to report the exact problem. It will not crash, but only draw nothing.

Also see 015cf2d