That would appear more frequent in higher difficulties. Things like
- a mole rat king (with a tilted crown that stays on its head for lols, even when he burrows underground)
- radscorpion alphas
- super radroaches
- king and queen stingwings
- boss bloatflies
- giant yao guai
and of course more behemoths and mirelurk queens, which are already a delight to fight.