Place PNGs for mark icons here:
- fire_0.png .. fire_5.png - levels for FIRE
- thunder_1.png .. thunder_5.png - Thunder Mark charge levels
- thunder_5_glow.png - pulsing full-charge overlay rendered for Thunder level 5
- immunity_1.png - immunity icon

Recommended size: 64x64 with alpha. The renderer uses entityTranslucent.
