If you take battle or effect damage while this card is in your GY: You can place this card from your GY in your Spell & Trap Zone as a face-up Continuous Trap. During the Main Phase, if this card is treated as a Continuous Trap: You can Tribute 1 "HERO" monster; Special Summon this card. If this card is Special Summoned from the Spell & Trap Zone: You can halve the ATK of 1 face-up monster on the field. You can only use each effect of "Vision HERO Poisoner" once per turn.
Use these cards to search Vision HERO Poisoner from your deck. Elemental HERO Blazeman, Vision HERO Vyon, and Neos Fusion are able to pitch Vision HERO Poisoner directly to your graveyard which can be more effective than adding him to your hand.
Aside from Normal Monsters and anime-exclusive cards, we've never gotten a card in Duel Links BEFORE the TCG. We've definitely had cards appear very soon after their TCG release, though, much quicker than Poisoner. Deus X-Krawler was 3 weeks, for example.
Not really. As of September 20, 2019 Poisoner could be used for Anteatereating Giant, Vision Hero Witch Raider, and Uria, Lord of Searing Flames but these decks have very little competitive potential. I guess you can make a few shekels with these decks on youtube though.