From: chaoshadou | #013*Nasus runs up*
Q.
Old Tiamat didn't proc on hit effects, and thus didn't give him Q stacks except on the original minion he hit. The new one has it's own healing effect, since it doesn't seem to proc any other lifesteal. I doubt they are going to let Nasus Q entire minion waves with Tiamat and get all the bonus damage.
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~{Always Sleeping}~