Pedal has just dropped off. How do I fix it with just a multitool and unlimited amounts of mud? Ta!

M520.

What dropped off? Pedal from crank? just screw back on. Pedal off axle then you may need some more tools

By the time you’ve bought tools, bearings & grease you’d have spent probably 1.5x the cost of a new set. 🙁
Cheaper SPD’s have a plastic collar that needs a special tool, & they usually just shatter when you try & undo them. I spent a bit more on M647’s for this reason.

£20 new on crc just get new.

Cold wet and gray. Pedal off spindles
Time to bail while I’m enjoying it.

Sounds like you are out on the trails with a smartphone. In which case clip it to your shoe and slide your foot onto the axel and ride home/to the car 🙁

Guessing plastic but broke? Spend an extra £10 and go to merlin for the m540 pedals. No special tools needed to service

But the 540 can only be fitted with an Allen key can’t it? No help to the op though.

Pedalled home one-footed on the roads; waiting by a hedgerow in the rain for a delivery from CRC didn’t appeal 🙂

The old M505 pedals require a special Shimano tool to reach in and undo the lock nut and adjust the cone. It costs approx £54.

http://www.chainreactioncycles.com/Models.aspx?ModelID=5730

Newer M520 needs a cheapo plastic tool to put in the vise and dismantle easily. It costs approx £2.

http://www.tweekscycles.com/Product.do?method=view&n=3339&p=34120&c=215&utm_source=Google&utm_medium=Base&utm_campaign=Cycle%20Tools

M520 is approx £20 new with cleats.
Keep your old parts…they are often used in other models and may be useful for spares/hoarding training.

PaulD