Tantalum is rare transition metal that your almost certainly using now. It’s used in capacitors in almost every modern computing device. This it is one of the metals most prized in the recycling of such devices. It’s not very toxic at low levels but can easily become so in high doses. It’s tied with the Tantulum elgans a sea bound slug that shares a similar name.
Tungsten is a very hard transition metal. It’s used in heating elements, mining and aerospace. It’s getting harder to source and mine and has become rarer in recent years.
Rhinoceros are large megafauna herbivores that are unfortunately endangered. It’s tied to Tungsten as they both have increased rarity and hardness.