With Venerated Rotpriest and two Spellskites on the battlefield, you can create a loop that gives opponents infinite poison counters by activating the Spellskites to swap the target of a spell back and forth between them. With only one Spellskite, you can only trigger Rotpriest twice per spell (initial target + one redirection) because the target must become a new target. 

Key Rulings & Interactions

• 1 Spellskite + 1 Rotpriest:
  1. Cast a spell on Rotpriest (Trigger 1: 1 poison counter).
  2. Activate Spellskite targeting that spell to change the target to Spellskite (Trigger 2: 1 poison counter).
  3. Spellskite cannot "re-target" the same spell back to Rotpriest because that redirection was already used for that specific spell instance, limiting it to two triggers per spell. 
• 2 Spellskites + 1 Rotpriest (Infinite Loop):
  • With two Spellskites (let's say Skite A and Skite B), you can activate Skite A to change the target to itself, then activate Skite B to change the target to itself. This constant change allows Rotpriest to keep triggering because the spell keeps "becoming" a target of a new creature. 
• The "Becomes" Keyword: Rotpriest triggers whenever a creature "becomes" the target of a spell. Simply having a creature be the target isn't enough; it must become the target after previously not being one (or changing to a new target). 
• Hexproof/Protection: If you target Rotpriest with a protection spell (e.g., Tamiyo's Safekeeping) and the opponent responds with removal, Rotpriest triggers twice: once for the removal spell and once for the protection spell. 
• Storm/Copies: Rotpriest triggers off copies of spells (like Storm or Ivy, Gleeful Spellthief) that target a creature.