If the creature returns to the battlefield attacking, it wasn’t declared as an attacking creature that turn. Abilities that trigger whenever a creature attacks, including the last ability granted by Meandered Towershell, won’t trigger.
2024-11-08
Playtest cards aren’t legal for play in any tournament format other than Mystery Booster Limited formats. On the other hand, we expect they will spice up a wide variety of non-tournament games (as long as everyone’s on the same page about using them!).
2024-11-08
Playtest cards use a modified version of game symbols, such as and . These modified symbols should be treated as the standard symbols during play.
2024-11-08
For many playtest cards, you’ll need to make a generous assumption that basic game rules would be updated to allow them to work. The Mystery Booster 2 Playtest Card Notes section (reproduced here in individual Gatherer rulings) provides guidance for fitting these cards into the existing rules structure.
Enchant creature
Enchanted creature has islandwalk and "Whenever this creature attacks, exile it and Meandered Towershell. Return it to the battlefield under your control tapped and attacking at the beginning of the declare attackers step on your next turn, then return Meandered Towershell to the battlefield under its owner's control attached to that creature."
As the creature returns to the battlefield because of the delayed triggered ability, its controller chooses which player, planeswalker, or battle it’s attacking. It doesn’t have to attack the same player, planeswalker, or battle that it was attacking when it was exiled.
and 
. These modified symbols should be treated as the standard symbols during play.