The Arctic Warbler is a very common winter visitor and passage migrant in Malaysia, traveling from its breeding grounds in Siberia, northern Asia, and Alaska to spend the winter months in Southeast Asia. While in the region, including Seberang Perai they can be found in various habitats, including forests and urban areas.
A small, greenish-olive warbler with a distinct long, pale supercilium (eyebrow), a dark eye line, and a stout bill with a yellowish base.

They are active insectivores, often seen in the canopy, but can be difficult to spot due to their, small size and fast movement. But once you learn the call you will realise it is fairly common all over Seberang Perai.

https://datazone.birdlife.org/species/factsheet/arctic-warbler-phylloscopus-borealis