I've been poisoned by the Nettle's needles,

And butchered by the Bramble,

The Hawthorn left me hacked to bits,

But unhindered do I ramble.

I took a thrashing from the Thistle,

And the Holly had me harried,

But the pain of Privet piercings pale,

To the weight that I have carried.

The Blackthorn's spears bloodied me,

I was gauged and grazed by Gorse,

The Dog Rose deals in rips and tears,

But my resolve knows no remorse.

The way is wild, the path it winds,

The slopes are sleaked with mud,

But the Lady I am looking for

Is worth each drop of blood.

In Sacred Groves she waits for me,

While I trudge on alone,

But fear not for my Lady,

Since King Arthur is a bard (albeit a frivolous one) in Welsh Myth, that technically means Arthur is a magician in some capacity.

Bards/Poets in Celtic Culture and Myth are combo of newscaster, historian, genealogist, prophet and entertainer. They are essentially lore keepers - Walking libraries for a mostly illiterate society. Which is why they are placed in an esteemed social status. They not only entertain but can prophesize the future, rouse one's companions to action and curse people with satires, on top of preserving knowledge through poetic forms.

Taliesin and Myrddin Wyllt are examples of from welsh lore. In Irish myth, there's Laidcenn, Niall (of the nine hostages)'s poet, and I remember some poet-warrior threatened to lampoon Cu Chulainn.

I think evidence that points to Arthur's magic is in the story Gwyn, Gwythyr and Creiddylad:

If you interpret Gwyn and Gwythyr as mortal men, Arthur magically oath-bound two men to fight each other until judgement day, granting them immortality in the process.

If you interpret Gwyn and Gwythyr are divine beings, then Arthur cursed two gods to fight each other annually and organized the seasons.

No matter how you cut it, Arthur is pretty magically strong. Other magical facts about Arthur include:

Welsh Triads saying Arthur had the ability to render the land infertile for seven years wherever he walks.

Arthur having an invisibility cloak, like Harry Potter. It was called "Gwenn", apparently.

Oral Folklore that says that Arthur can shapeshift into a raven or chough. Which is why it's bad luck to kill one.

Creiddylad

I sing for the May Queen,

Head wreathed in fragrant wildflowers

And palms bearing sweet mead

Awaken summer's lusty opulence,

Radiant daughter of Lludd

Most majestic maiden of all the Isles!

Gaze upon this year's players with favor,

As they water the Earth with their blood

And vie for your silvery hand

Guide our steps as we circle the roaring flames,

Warm our bodies and beds with May's melody,

Like your passionate union with Gwyn

Grant us the vigor of summer's sun,

Bless us with the youthful blossom of beauty.

the women of welsh mythology 

Creiddylad, the Welsh goddess of flowers