If heads, prevent all effects of an attack, including damage, done to during your opponent's next turn
The Helm checks every single time an individual card is milled with it to see if either of those conditions are meant
Here's one that's popular in Standard right now: On turn two, the Advocate is a 2/3 with vigilance
If an Ally entering at the same time as Katara (including Katara herself) causes a triggered ability of an Ally you control to trigger, that ability triggers an additional time
Oshawott Illustration Rare, 105/086 Of course, heres one of those cards thats valuable simply because its aesthetically stunning
Summon: Kujata This six-drop 7/5 and trample and haste is next with an ETB to Bolt two dorks, force three to not attack and then discard one, draw two - great card flow, and then shoot your foes equal to the cost of what you discarded