Could you give annotated examples regarding the grammar of a sentence in classical Chinese where 爾 is used as an adverbial suffix?
爾/尔 in Classical Chinese can be used similarly to 然, roughly meaning "thus/so/in such a manner", changing the word to which it's suffixed into an adverb. Here's an example from Mencius 孟子 we can analyze:


  一簞食，一豆羹：得之則生，弗得則死。嘑爾而與之，行道之人弗受；蹴爾而與之，乞人不屑也。


My attempt at a faithful English translation:


  A basket of rice, a platter of soup: with them one survives; without them one dies. When offered insultingly, a vagabond would not accept them; when offered trampled, even a beggar would reject them.


Here we see 爾 modify the verbs 嘑 (to insult) and 蹴 (to trample) to convert them into adverbs that indicate how the food is offered.