Corrupted Fin of the First Spear is a Dota 2 item of Immortal rarity. On DotaLoot you can win it in free giveaways or earn it with Battle Pass levels.
You can get Corrupted Fin of the First Spear for free in daily DotaLoot giveaways or with Battle Pass levels. The fastest way is opening cases — noticeably cheaper than buying it on the market.