Magius listened, and nodded. This sort of thing was fun. Working together with someone as determined as he to work it out, and who wanted to be able to do it, and who had the knowledge and determination to use that knowledge, well, it was fantastic!
He nodded, and hoped the spell would not drain the other man too much.
He concentrated on his memory, and staggered as he felt the power erupt from the other man, and with a will reached out, seeing and feeling the doe, and the power in it and willing his own power to join it, flooding in and shifting the patronus into the shield he'd made before, one larger and more shimmering than the last.
And it lasted longer as well, as Magius bent his will, letting his magic flow, and knowing this would cost him spells, even as he knew, in this instance, that didn't matter. When it finally faded, he slumped a little, feeling drained, magically and physically.
He swallowed and glanced at Snape. "Are-- are you okay? That was rather intense."