GRAMMAR C1

IPT Advanced
Although a little bit disorganised, you can find lots of helpful stuff and grammar practice from New English File Advanced on this Wordpress blog:

Gerunds and full infinitives as subjects and objects

Gerunds and full infinitives as subjects and objects function and mean pretty much the same but maybe when you use an infinitive it sounds like more abstract. Check this explanation on English Language Centre and do the activities online.

Who and Whom

Visit ​Grammarly to get a straightforward explanation and some activities to check your understanding of the theory. Find some activities to practise who/whom on My English Pages.

Would and used to

Find a good explanation on BBC World Service (including audio and transcript) and some grammar tests on Learning English/British Council

Question tags intonation

Learn and practise the two different kinds of Questions tags intonation on BBC World Service: http://www.bbc.co.uk/worldservice/learningenglish/radio/specials/1634_gramchallenge2/ (click on the right).
Listen to examples and practise: http://www.bbc.co.uk/worldservice/learningenglish/radio/specials/1634_gramchallenge2/page2.shtml
Decide whether the question tags are real or they are trying to check information: http://www.bbc.co.uk/worldservice/learningenglish/radio/specials/1634_gramchallenge2/page3.shtml
Find more practise on question tags on the Upper/intermediate uses section ​

Ellipsis and Substitution: so and not

Get a summary on substitution: so and not on downloads. Find some activities on Ellipis and Substitution, lesson 6B, at Oxford University Find an activity on substitution with "so" at Warwick. Find many more exercises on substitution and ellipsis on LLAS (Centre of Languages and Linguistic area Studies, University of Southampton) click next after finishing every activity.

Participle clauses

 Visit EnglishLingolia to get an explanation, examples, and online activities on Participle clauses in English.

Verb Inversion in English

Visit eitherLearn English Today , To learn English or English Tenses to practise Verb Inversion in English

CLEFT SENTENCES

Get a detailed explanation and some exercises on cleft sentences clicking on Grammar Quizzes (left) and some more exercises on Carmenlu's blog (right)

PASSIVE VOICE

Please, visit Edumantra to get a good explanation and lots of solved and unsolved activities. The British Council has a quite straightforward explanation with some online activities.
A good explanation to download is this one on RWC.  Lingoda also offers a pdf file with activities and keys.