This is one of the many elixirs that can be made by cooking critters with monster parts.

Recipe: ?Fireproof lizard + monster parts

Effect:? Fireproof (not to be confused with Heat Resistance). Fireproof will protect you from the specific fiery heat of the Eldin Region's Death Mountain that will literally light you on fire. However, this elixir cannot protect against heat from dry areas like the Gerudo Wasteland.

If you do not wish to craft one yourself, you can buy them either at Goron City or the Foothill Stable on the road just outside of Death Mountain.

This recipe will produce a Lv. 1 elixir (10:30 min duration):
1x Fireproof Lizard
1x Red Chuchu Jelly
1x Moblin Fang
1x Lizalfos Horn
1x Bokoblin Guts