Most of your abilities (including your ultimate) have long and noticeable startup times. Torvald's Nullify will interrupt those, so wait until he uses it or buy Resilience to reduce the downtime he can cause.
Lex deals too much damage to fight on your own. If you're under attack from him, use Shadow Travel and move to a safer location, then regroup with your team.
If you suspect Mal'Damba has his ult ready, try to space yourself a bit from the rest of your team. Dread Serpent will knock you out of the air if you're flying, and its hitbox persists for a few seconds after it triggers.