All while tapping down an opponents creature, which you can do defensively to keep it from attacking you, offensively to push through attackers, or politically with wheeling and dealing
In a 1-versus-1 game, Mangara slows down their game plan and keeps you alive longer, as they would likely stick to 1 attacker and 1 spell on their turn (unless theyre willing to let you draw)
The idea of him in my mind was someone who came and brought winter with him (representing the difficulty supporting large numbers of creatures) and then when enough time and seasons happened he became aware of what he was, and began his planeswalking
Copying an X-cost spell will also copy the value of X you paid into the original
If the roll happened because of a replacement effect as part of a static ability (for example, the ability that sets Vedalken Squirrel-Whacker's base power and toughness), that ability isn't copied