I will have a small group of my soldiers, perhaps five, take a light amount of plastic explosives, use magic to transform them and the explosives into fish small enough to swim through the river without seeming out-of-place, while a second small strike team(ten) heads up the side of the hill just to the left of the picture's edge transfigured into small snakes, placing more explosives at the bottom of the cliff. They will detonate the cliff explosives once safely away, giving the distraction needed for the river group to get in and place their explosives.
Once the river group plants their explosives and gets out, a third small group (three) will come in from the road, looking like ragged, wounded civilians. They will speak of an attack made upon a nearby town still allied to the owners of the bunker, and request help. Either:
1: The bunker takes men to go and aid the town, thereby lessening the amount of soldiers available to defend the bunker, or
2: They will deny the civilians' requests and demand they leave, still granting a distraction for snipers to take out any guards on the roof.
The river group's explosives will now be detonated, disabling the hydro-power plant and thus the automated defenses. The main force will then come forth, split between swimming up the river, slithering up the hill near the cliff and flying to the now cleared roof. They'll flank the bunker while still hidden, the snake group returning to normal once up the ruined cliff, and the river group returning to normal once inside the power plant, and the birds once on the roof. The snake group will enter from the left side and secure that entrance, the river group securing the water route, and the bird group securing the roof. The birds will then set up snipers on the roof to cover the front exit, as well as any rear exits.
The river group will use the river-water to freeze foes, or to lock enemies in rooms for gassing.
