Pretty Damn awful, PyEVM Virtual Machine debugger. Using a custom opdcode set in Vyper ;)

pre_vdb_ipdb.py

def debug_opcode(computation):
    print('YOUR ARE HERE!')
    import ipdb; ipdb.set_trace()
    
import evm
from evm.vm.opcode import as_opcode
from vyper.opcodes import opcodes as vyper_opcodes
from evm.vm.forks.byzantium.computation import ByzantiumComputation
opcodes = ByzantiumComputation.opcodes.copy()
opcodes[vyper_opcodes['DEBUG'][0]] = as_opcode(
    logic_fn=debug_opcode,
    mnemonic="DEBUG",
    gas_cost=0
)
setattr(evm.vm.forks.byzantium.computation.ByzantiumComputation, 'opcodes', opcodes)

Thanks for replies. I will check it out.