Gweithgaredd 37

In this example, the preposition i has conjugated, iddo.  There is a soft mutation after some/most prepositions and conjugated prepositions, e.g.

Aeth Efan i'r gwely ar ôl iddo gyrraedd adref.

Mae'n flin ganddo gyhoeddi'r newyddion trist.

The suffixes (endings) for the prepositions can be found by clicking here.

The table of mutations can be found by clicking here.

uchel is an irregular adjective.   When using uchel in a comparative context, we use uwch.  Here are some irregular adjectives:

The subject/person completing the action is not indicated in an impersonal verb's suffix (ending). 

-ir, -wyd and -id are the most commonly used suffixes for impersonal verb forms.  

The impersonal verb forms can be shown as follows:

When using concise forms of the verb, the normal sentence structure in Welsh is Verb + Subject + Object, e.g.
Rhedodd y ferch y ras.
Ysgrifennodd y bardd gerdd.
Dylai'r plant gael gwersi.

However, sentences which include impersonal verbs do not follow this pattern. 

When using the impersonal tense, the object follows the verb and the subject/person completing the action is included after gan, e.g.
Rhedwyd ras gan y ferch.
Ysgrifennwyd y gerdd gan y bardd.
Cafwyd amser da gan bawb.

Note also that there is no soft mutation after an impersonal verb (unlike personal verbs), e.g.
Ysgrifennwyd cerdd gan y bardd.
Ysgrifennodd y bardd gerdd.

dylai (he/she/it should) this is a defective or incomplete verb and doesn't have the full range of tenses:

When using the negative forms, the d takes a soft mutation and is replaced with a dd and ddim is also added, e.g.
Ddylwn i ddim aros yn rhy hir.

Welais i mohoni - Ddim / mo / mo'r
When the object is indefinite (e.g. a film, a book etc.), use ddim, e.g.
Welais i ddim ffilm neithiwr. (I didn't see a film last night.)

When the object is definite (e.g. the film, the book), use mo'r, e.g.
Welais i mo'r ffilm neithiwr. (I didn't see the film last night.)

When the object is named (e.g. Star Wars, War and Peace), use mo, e.g.
Welais i mo Star Wars neithiwr. (I didn't see Star Wars last night.)

When the definite object is a pronoun (he, she, them …), i.e. a word used to replace a noun that has already been mentioned, the preposition o conjugates as follows in a negative context:

The endings for the short form of the imperfect tense are as follows.

In this case, the first person singular ending is required, e.g.

gallwn i, cofiwn i, cerddwn i

Gwneud is an irregular verb and it is conjugated as follows:

Remember

There is a soft mutation at the start of the negative form, e.g.

ni allwn i, allet ti ddim, ni wnaem ni

The table of mutations can be found by clicking here.