Learn Hardcore Filipino: Sasakay tayo ng tren para mas mabilis.

tayo = we/us (including the listener).
Example: Sasakay tayo ng tren... = You and I (and possibly others) will take the train.
kami = we/us (excluding the listener).
Example: Sasakay kami ng tren... = We will take the train (but not you).

What tense/aspect is sasakay and how is it formed from the root sakay?

Filipino marks aspect more than tense. For the root sakay (to ride), actor-focus forms are:

Completed (past): sumakay
Incomplete (present/progressive): sumasakay
Contemplated (future/intent): sasakay

Note how the -um- infix appears in past/present (su-m-a…) but drops in the future, which uses reduplication of the first syllable: sa + sakay → sasakay.

Can Sasakay tayo... mean both We will ride... and Let’s ride...?

Yes. Context and intonation decide:

Statement/plan: Bukas, sasakay tayo ng tren.
Suggestion: Sasakay tayo ng tren, para mas mabilis. (friendly, suggestive tone) You can make the suggestion explicit with Tara or na: Tara, sumakay tayo ng tren, or Sasakay na lang tayo ng tren.

Why is it ng tren and not sa tren?

sumakay/sasakay + ng + vehicle = ride something as a means of transport (mode/instrument).
Example: Sasakay tayo ng tren. (We’ll take the train.)
sumakay/sasakay + sa + vehicle/place = get on/board a specific vehicle or at a location (destination/locative).
Example: Sasakay tayo sa tren na ito. (We’ll board this train.)

Using ng tren sounds like choosing a mode of travel; sa tren points to a particular train or boarding place.

What’s the difference between ng and nang, and which one is in the sentence?

In the sentence you need ng: Sasakay tayo ng tren... (ng marks the non-focused object/thing being ridden).
ng is for objects, possession, and often corresponds to the English unmarked object or of.
nang links to adverbs/degree or means when/as.
Example (adverbial): Sumakay kami nang mabilis. (We boarded quickly.) Pronunciation note: ng is pronounced like nang.

Could I say Sasakyan natin ang tren instead? What changes?

Yes, that’s the object-focus form using sakyan (-an affix). Nuance:

Sasakay tayo ng tren... (actor-focus): focuses on the doer (we).
Sasakyan natin ang tren... (object-focus): focuses on the train as the topic. Also note the pronoun change: tayo (actor-focus subject) → natin (non-topic actor in object-focus).

Is the word order Tayo ay sasakay ng tren... acceptable?

Yes. Tayo ay sasakay ng tren... is grammatical but more formal or emphatic (topic-fronting with ay). The most natural conversational order keeps the pronoun right after the verb: Sasakay tayo ng tren...

How does para work here? When do I use para, para sa, para kay, or upang?

para + clause (purpose): para mas mabilis (so it’s faster).
para sa + noun (for something): para sa biyahe (for the trip).
para kay + person (for someone): para kay Ana.
upang + clause = a more formal synonym of para: upang mas mabilis.

What does mas mabilis mean, and do I need to say “than something”?

mas + adjective = more + adjective → mas mabilis = faster.
You can optionally state the comparison: mas mabilis kaysa (sa) bus (faster than the bus).
Without kaysa, the comparison is understood from context (faster than other options we’re considering).

Is it okay that para mas mabilis doesn’t have a verb? Should it be para mas mabilis tayong makarating?

It’s fine as-is; Filipino often omits predictable parts. The full ideas could be:

para mas mabilis tayong makarating (so we can arrive faster), or
para mas mabilis ang biyahe (so the trip is faster). The short para mas mabilis is natural when the rest is obvious.

Do I need na anywhere, like Sasakay na tayo or para mas mabilis na?

na often means now/already/anymore, or softens suggestions: Sasakay na tayo (let’s ride now).
na lang means just/instead: Sasakay na lang tayo ng tren (let’s just take the train).
You don’t add na to mas mabilis here unless it’s linking to a following noun, e.g., mas mabilis na biyahe (a faster trip).

How is everything pronounced and stressed?

sasakay: sa-sa-KAY
tayo: TÁ-yo
ng: pronounced as NANG (nasal ng)
tren: tren
para: PÁ-ra
mas: mas
mabilis: ma-bi-LÍS

Can I drop ng and say Sasakay tayo tren?

No. You need the case marker. Use either:

Sasakay tayo ng tren (mode of transport), or
Sasakay tayo sa tren (board a specific train).

Does ng tren mean “a train” or “the train”? How do I be specific?

ng tren is generally indefinite/generic (by train). To be specific, use sa plus a modifier:

Sasakay tayo sa tren na iyon (that train).
Or name the line/station: Sasakay tayo sa MRT sa Ayala Station.

Is mabilis an adjective or an adverb? Do I need nang before it?

mabilis can be a predicate adjective: para mas mabilis (so it’s faster).
As an adverb modifying a verb, use nang: Sumakay kami nang mabilis (we boarded quickly). In your sentence it’s a predicate adjective in a purpose clause, so no nang needed.

Is it natural to say mag-tren or use English train instead of tren?

Standard Filipino uses tren and the verb sumakay: Sumakay/Sasakay tayo ng tren.
Colloquially, some say mag-tren (to take the train), but it’s more casual/Taglish.
Using English train in Taglish is common in speech: Sasakay tayo ng train, but tren is the Filipino word.