Since he essentially gains +3/+3 each time he takes damage, and gives you three rad counters at the same time, any repeatable ping effect can grow Strong to obscene proportions and Mill your entire deck, opening the doors for a Thassas Oracle win the next turn
Even something like Urza's Command can be very powerful if the correct critical mass of playable artifacts is hit, and having access to counterspells to stop Farewell is also big game
The best of these options is Cultist of the Absolute
These cards range in value, with the cheapest being $500 and the most expensive being $2400
How about drawing some cards
The Revelations of Ezio is pretty narrow and wants to be in an Assassin deck, and as a longtime Magic player, I smile at Chapter Is callback to Royal Assassin killing a tapped creature