Learn Hardcore German: Ich überrasche meinen Freund.

It’s in the accusative case because überraschen is a transitive verb that takes a direct object, and direct objects in German are marked with the accusative.

Why is it meinen Freund and not mein Freund?

Freund is masculine singular, and possessive pronouns like mein follow the same declension as ein. In the masculine accusative, you add -en, so mein becomes meinen.

Why is the verb überrasche written as one word, instead of splitting über off like in aufstehen → stehen auf?

Because über here is an inseparable prefix. Inseparable prefixes (be-, ent-, er-, ver-, zer-, über-, etc.) always stay attached to the verb in all finite forms, never moving to the end.

Where is the word stress in überrasche, and how can I tell?

The stress falls on the verb stem: überRASche. Inseparable prefixes do not carry stress, so the emphasis is on rasch.

Can I drop the final -e in überrasche and say ich überrasch meinen Freund?

In very colloquial spoken German you might hear ich überrasch, but in Standard German (especially in writing or formal speech) you keep the -e ending in the first-person singular: ich überrasche.

How would I form the past tense of Ich überrasche meinen Freund?

– Simple past (Präteritum): Ich überraschte meinen Freund.
– Present perfect (Perfekt): Ich habe meinen Freund überrascht.
Überraschen is a regular (weak) verb, so its past participle is überrascht (ge-…-t).

Why is there no preposition before meinen Freund?

Überraschen is a fully transitive verb and takes a direct object in the accusative. There’s no need for a preposition — unlike verbs that govern their objects with a preposition (e.g. warten auf, teilnehmen an).

How do I express “I will surprise my friend” in German?

You have two options:

Use the present to indicate a near future: Ich überrasche meinen Freund morgen.
Use the future tense with werden: Ich werde meinen Freund überraschen.