Spells or other one-time effects that modify attack will not affect Shardplate Behemoth. For example, targeting a Behemoth with Electro Net will not reduce its attack.
Shardplate Behemoth has more complex interactions with static effects that modify attack. For example, if a Nexus Aeronaut and a Shardplate Behemoth are both on the field, their relative position will determine whether or not Behemoth gets a higher attack value. When multiple static effects are in play at the same time, they are applied from left to right. Since Aeronaut's and Behemoth's abilities are both static effects, their positioning influences the resulting board state. If Shardplate Behemoth is to the left of Nexus Aeronaut, it will first set its attack equal to its health, then it will recieve +attack from Aeronaut. If Shardplate Behemoth is to the right of Nexus Aeronaut, the +attack effect will be applied first, then Behemoth will set its attack equal to its health, negating the bonus.
Stats prior to phase 1 of the rebalance.