One of the rare magical spells in TF2 is "meteor shower," which summons, well, meteors. None of the cast can tank the entire spell, but even the frailest class; the Scout, can tank it for a bit, so it should be reasonable to scale the mercs to one meteor.
Scout's height = 181.6 centimeters = 202 pixels
Meteor Radius = 25.7/2 = 12.85 pixels = 11.5522772277 centimeters
11.5522772277^3 * Pi * (4/3) = 6,457.90149884 cm^3, or 0.00645790149 M^3
Iron Metorite Density is ~8 grams/cm^3, or 8,000 Kg/M^3
0.00645790149 * 8,000 = 51.6632119908 Kilograms
Pretty small meteors, but what makes this feat impressive isn't their size, it's their speed, as all magic spells (Well, not all of them, but meteor shower is one of them) in TF2 have a speed of 1,019.8 Hammer units/second, which is very close to the speed of the righteous bison's projectiles, which, y'know, are nearly light speed, this is consistent with the meteors being capable of tagging the mercs, who can dodge the righteous bison's projectiles
Righteous Bison projectiles = 0.9999999896 C = 1,200 HU/S
Meteor Shower = 1,019.8 HU/S = 0.849833333333 C
Using this speed gets the meteors' relativistic kinetic energy to be:
4.1666169081*10^18 Joules, 995.84534 Megatons of TNT, 7-A, Mountain level+
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Thanks to El rapero de tf2 for the pixel scaling here
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Sniper = 1.879 Meters = 114 pixels
Meteor = 50 pixels = 0.82412280702 Meters
Meteor radius = 0.82412280702/2 = 0.41206140351 Meters
0.41206140351^3 * Pi * (4/3) = 0.293072063124 M^3
8,000 * 0.293072063124 = 2,344.57650499 Kilograms
And now comparing the meteor's 1,019.8 Hu/s speed to the Pomson 6000, which fires "rapid pulses of high-amplitude radiation," AKA light speed projectiles, which move at 1,200 Hu/s
1019.8/1200 = 0.849833333333 C
Using a RKE calcualtor and the above mass and velocity gets:
1.890891358810^20 Joules, 45.19339 Gigatons of TNT, 6-C, Island level