Does Spellsong work with other Equipment like Boneshiver or Trinity Force?

No, Svellsongur does not work with other equipment like Boneshiver or Trinity Force in the way you are likely intending.

According to official RiftJudge FAQs, Svellsongur only copies the text that is physically printed on the unit card it is attached to. It does not copy any abilities, keywords, or effects that are granted to that unit by other attached equipment (such as the "When I conquer, channel 1 rune exhausted" text from Boneshiver or "When I hold, score 1 point" from Trinity Force).

In short:

• Svellsongur copies: Only the original printed text of the unit.
• Svellsongur ignores: Text granted by other gear, spells, or battlefield effects.

This interaction is intended by the designers to ensure that the order in which you attach equipment does not create complex or unintentional rules outcomes.