Its an endless army in a can for Aggro or Aristocrats decks, in a similar vein to Bitterblossom
The sacrifice ability occasionally came in handy, guarding against mass removal even though it was never the primary motivating factor, and it was hard for decks running him to justify keeping the necessary mana untapped until very late in the game
Merlin is here to find those must-have one-offs straight away
If there is an additional combat phase that turn, or if another player gains control of it before it stops being goaded, it must attack again if able
For example, Esper Sentinel can be dropped on turn one, and as you attach Equipment later you'll be more and more likely to draw cards every turn
There is a picture of a new Sisu on boosters (with a red aura), booster boxes, and the trove